[PATCH v2 0/3] can: length: fix definitions and add bit length calculation

[PATCH v2 0/3] can: length: fix definitions and add bit length calculation

[Vincent Mailhol]

When created in [1], frames length definitions were added to implement
byte queue limits (bql). Because bql expects lengths in bytes, bit
length definitions were not considered back then.
    
Recently, a need to refer to the exact frame length in bits, with CAN
bit stuffing, appeared in [2].

This series introduces can_frame_bits(): an inline function that can
calculate the exact size of a CAN(-FD) frame in bits with or without
bitsuffing.

The review of v1, pointed out a few discrepancies of the current
length definitions. This series got extended to fix those
discrepancies.

[1] commit 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce
    function to get data length of frame in data link layer")
Link: https://git.kernel.org/torvalds/c/85d99c3e2a13

[2] RE: [PATCH] can: mcp251xfd: Increase poll timeout
Link: https://lore.kernel.org/linux-can/BL3PR11MB64846C83ACD04E9330B0FE66FB729@BL3PR11MB6484.namprd11.prod.outlook.com/


* Changelog *

v1 -> v2:

  * as suggested by Thomas Kopp, add a new patch to the series to fix
    the stuff bit count and the fixed stuff bits definitions

  * and another patch to fix documentation of the Remote Request
    Substitution (RRS).

  * refactor the length definition. Instead of using individual macro,
    rely on an inline function. One reason is to minimize the number
    of definitions. An other reason is that because the dynamic bit
    stuff is calculated differently for CAN and CAN-FD, it is just not
    possible to multiply the existing CANFD_FRAME_OVERHEAD_SFF/EFF by
    the overhead ratio to get the bitsuffing: for CAN-FD, the CRC
    field is already stuffed by the fix stuff bits and is out of scope
    of the dynamic bitstuffing.

Link: https://lore.kernel.org/linux-can/20230507155506.3179711-1-mailhol.vincent@wanadoo.fr/T/#u

Vincent Mailhol (3):
  can: length: fix bitstuffing count
  can: length: fix description of the RRS field
  can: length: refactor frame lengths definition to add size in bits

 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 323 +++++++++++++++++++++++++----------
 2 files changed, 238 insertions(+), 100 deletions(-)

-- 
2.25.1

[PATCH v2 1/3] can: length: fix bitstuffing count

[Vincent Mailhol]

The Stuff Bit Count is always coded on 4 bits (ref [1]). Update the
Stuff Bit Count size accordingly.

In addition, the CRC fields of CAN FD Frames contain stuff bits at
fixed positions call fixed stuff bits [2]. The CRC field starts with a
fixed stuff bit and then has another fixed stuff bit after each fourth
bit [2], which allow us to derive this formula:

  FSB count = 1 + round_down(len(CRC field)/4)

The length of the CRC field is [1]:

  len(CRC field) = len(Stuff Bit Count) + len(CRC)
                 = 4 + len(CRC)

with len(CRC) either 17 or 21 bits depending of the payload length.

In conclusion, for CRC17:

  FSB count = 1 + round_down((4 + 17)/4)
            = 6

and for CRC 21:

  FSB count = 1 + round_down((4 + 21)/4)
            = 7

Add a Fixed Stuff bits (FSB) field with above values and update
CANFD_FRAME_OVERHEAD_SFF and CANFD_FRAME_OVERHEAD_EFF accordingly.

[1] ISO 11898-1:2015 section 10.4.2.6 "CRC field":

  The CRC field shall contain the CRC sequence followed by a recessive
  CRC delimiter. For FD Frames, the CRC field shall also contain the
  stuff count.

  Stuff count

  If FD Frames, the stuff count shall be at the beginning of the CRC
  field. It shall consist of the stuff bit count modulo 8 in a 3-bit
  gray code followed by a parity bit [...]

[2] ISO 11898-1:2015 paragraph 10.5 "Frame coding":

  In the CRC field of FD Frames, the stuff bits shall be inserted at
  fixed positions; they are called field stuff bits. There shall be a
  fixed stuff bit before the first bit of the stuff count, even if the
  last bits of the preceding field are a sequence of five consecutive
  bits of identical value, there shall be only the fixed stuff bit,
  there shall not be two consecutive stuff bits. A further fixed stuff
  bit shall be inserted after each fourth bit of the CRC field [...]

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 include/linux/can/length.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 69336549d24f..b8c12c83bc51 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -72,17 +72,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
+#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
 
 /*
  * Size of a CAN-FD Extended Frame
@@ -101,17 +102,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
+#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
 
 /*
  * Maximum size of a Classical CAN frame
-- 
2.25.1

[PATCH v2 2/3] can: length: fix description of the RRS field

[Vincent Mailhol]

The CAN-FD frames only have one reserved bit. The bit corresponding to
Classical CAN frame's RTR bit is called the "Remote Request
Substitution (RRS)" [1].

N.B. The RRS is not to be confused with the Substitute remote request
(SRR).

Fix the description in the CANFD_FRAME_OVERHEAD_SFF/EFF.

The total remains unchange, so this is just a documentation fix.

In addition to the above add myself as copyright owner for 2020 (as
coauthor of the initial version, c.f. Fixes tag).

[1] ISO 11898-1:2015 paragraph 10.4.2.3 "Arbitration field":

  RSS bit [only in FD Frames]

    The RRS bit shall be transmitted in fD Frames at the position of
    the RTR bit in Classical Frames. The RRS bit shall be transmitted
    dominant, but receivers shall accept recessive and dominant RRS
    bits.

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 include/linux/can/length.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index b8c12c83bc51..521fdbce2d69 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
+ * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
@@ -64,7 +65,7 @@
  * ---------------------------------------------------------
  * Start-of-frame			1
  * Identifier				11
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Identifier extension bit (IDE)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
@@ -95,7 +96,7 @@
  * Substitute remote request (SRR)	1
  * Identifier extension bit (IDE)	1
  * Identifier B				18
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
  * Bit Rate Switch (BRS)		1
-- 
2.25.1

[PATCH v2 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent Mailhol]

Introduce a method to calculate the exact size in bits of a CAN(-FD)
frame with or without dynamic bitsuffing.

These are all the possible combinations taken into account:

  - Classical CAN or CAN-FD
  - Standard or Extended frame format
  - CAN-FD CRC17 or CRC21
  - Include or not intermission

Instead of doing several macro definitions, declare the
can_frame_bits() static inline function. To this extend, do a full
refactoring of the length definitions.

If given integer constant expressions as argument, can_frame_bits()
folds into a compile time constant expression, giving no penalty over
the use of macros.

Also add the can_frame_bytes(). This function replaces the existing
macro:

  - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
  - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
  - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
  - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)

The different frame lengths (including intermission) are as follow:

   Frame type				bits	bytes
  ----------------------------------------------------------
   Classic CAN SFF no-bitstuffing	111	14
   Classic CAN EFF no-bitstuffing	131	17
   Classic CAN SFF bitstuffing		135	17
   Classic CAN EFF bitstuffing		160	20
   CAN-FD SFF no-bitstuffing		579	73
   CAN-FD EFF no-bitstuffing		598	75
   CAN-FD SFF bitstuffing		712	89
   CAN-FD EFF bitstuffing		736	92

The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept to be
used in const struct declarations (folding of can_frame_bytes() occurs
too late in the compilation to be used in struct declarations).

In addition to the above:

 - Use ISO 11898-1:2015 definitions for the name of the CAN frame
   fields.
 - Include linux/bits.h for use of BITS_PER_BYTE.
 - Include linux/math.h for use of mult_frac() and
   DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
   patch, but the include was previously omitted.
 - Add copyright 2023 for myself.

[1] commit 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce
    function to get data length of frame in data link layer")
Link: https://git.kernel.org/torvalds/c/85d99c3e2a13

[2] RE: [PATCH] can: mcp251xfd: Increase poll timeout
Link: https://lore.kernel.org/linux-can/BL3PR11MB64846C83ACD04E9330B0FE66FB729@BL3PR11MB6484.namprd11.prod.outlook.com/

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
In case you ask, here is the proof that can_frame_bits() folds into
a compile time constant expression.

This file:

  #include <linux/can/length.h>

  unsigned int canfd_max_len_bitsuffing(void)
  {
	return can_frame_bytes(true, true, true, CANFD_MAX_DLEN);
  }

Produces this assembly code:

  0000000000000010 <canfd_max_len_bitsuffing>:
    10:	f3 0f 1e fa          	endbr64
    14:	b8 5c 00 00 00       	mov    $0x5c,%eax
    19:	e9 00 00 00 00       	jmpq   1e <canfd_max_len_bitsuffing+0xe>

where 0x5c corresponds to the expected value of 92 bytes.
---
 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 326 +++++++++++++++++++++++++----------
 2 files changed, 238 insertions(+), 103 deletions(-)

diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
index b48140b1102e..b7f4d76dd444 100644
--- a/drivers/net/can/dev/length.c
+++ b/drivers/net/can/dev/length.c
@@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
 	else
 		len = cf->len;
 
-	if (can_is_canfd_skb(skb)) {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CANFD_FRAME_OVERHEAD_EFF;
-		else
-			len += CANFD_FRAME_OVERHEAD_SFF;
-	} else {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CAN_FRAME_OVERHEAD_EFF;
-		else
-			len += CAN_FRAME_OVERHEAD_SFF;
-	}
-
-	return len;
+	return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,
+			       false, len);
 }
 EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 521fdbce2d69..7518117ee5fc 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,132 +1,278 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
- * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
+ * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
 #define _CAN_LENGTH_H
 
+#include <linux/bits.h>
 #include <linux/can.h>
 #include <linux/can/netlink.h>
+#include <linux/math.h>
 
 /*
- * Size of a Classical CAN Standard Frame
+ * Size of a Classical CAN Standard Frame header in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicatior (FDF)		1
+ *	Data Length Code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CAN_FRAME_HEADER_SFF_BITS 19
+
+/*
+ * Size of a Classical CAN Extended Frame header in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	FD Format indicatior (FDF)		1
+ *	Reserved bit (r0)			1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CAN_FRAME_HEADER_EFF_BITS 39
+
+/*
+ * Size of a CAN-FD Standard Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_SFF_BITS 22
+
+/*
+ * Size of a CAN-FD Extended Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_EFF_BITS 41
+
+/*
+ * Size of a CAN CRC Field in bits
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * CRC sequence (CRC15)			15
+ * CRC Delimiter			1
+ *
+ * ignoring bitstuffing
+ */
+#define CAN_FRAME_CRC_FIELD_BITS 16
+
+/*
+ * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Stuff Count				4
+ * CRC Sequence (CRC17)			17
+ * CRC Delimiter			1
+ * Fixed stuff bits			6
+ */
+#define CANFD_FRAME_CRC17_FIELD_BITS 28
+
+/*
+ * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Stuff Count				4
+ * CRC sequence (CRC21)			21
+ * CRC Delimiter			1
+ * Fixed stuff bits			7
+ */
+#define CANFD_FRAME_CRC21_FIELD_BITS 33
+
+/*
+ * Size of a CAN(-FD) Frame footer in bits
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote transmission request (RTR)	1
- * Identifier extension bit (IDE)	1
- * Reserved bit (r0)			1
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
  * ACK slot				1
  * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * End Of Frame (EOF)			7
  *
- * rounded up and ignoring bitstuffing
+ * including all fields following the CRC field
  */
-#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+#define CAN_FRAME_FOOTER_BITS 9
 
 /*
- * Size of a Classical CAN Extended Frame
- *
- * Name of Field			Bits
- * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote transmission request (RTR)	1
- * Reserved bits (r1, r0)		2
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * rounded up and ignoring bitstuffing
+ * First part of the Inter Frame Space
+ * (a.k.a. IMF - intermission field)
  */
-#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+#define CAN_INTERMISSION_BITS 3
 
 /*
- * Size of a CAN-FD Standard Frame
+ * CAN bit stuffing overhead multiplication factor
  *
- * Name of Field			Bits
- * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote Request Substitution (RRS)	1
- * Identifier extension bit (IDE)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * The worst bit stuffing case is a sequence in which dominant and
+ * recessive bits alternate every four bits:
  *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
+ *   Destuffed: 1 1111  0000  1111  0000  1111
+ *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
+ *
+ * Nomenclature:
+ *
+ *  - "0": dominant bit
+ *  - "o": dominant stuff bit
+ *  - "1": recessive bit
+ *  - "i": recessive stuff bit
+ *
+ * Ignoring the first bit, one stuff bit is added every four bits
+ * giving us an overhead of 1/4 = 0.25.
  */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
+#define can_bit_stuffing_overhead(stream_len) mult_frac(stream_len, 1, 4)
+
+/**
+ * can_frame_bits() - Calculate the number of bits in on the wire in a
+ *	CAN frame
+ * @is_eff: true: Extended Frame; false: Standard Frame.
+ * @bitstuffing: if true, calculate the bitsuffing worst case, if
+ *	false, calculated the bitsuffing best case (no dynamic
+ *	bitsuffing). Fixed stuff bits always get included.
+ * @intermission: if and only if true, include the inter frame space
+ *	assuming no bus idle (i.e. only the intermission gets added).
+ * @data_len: length of the data field in bytes. Correspond to
+ *	can(fd)_frame->len. Should be zero for remote frames. No
+ *	sanitization is done on @data_len.
+ *
+ * Return: the numbers of bits on the wire of a CAN frame.
+ */
+static inline
+unsigned int can_frame_bits(bool is_fd, bool is_eff,
+			    bool bitstuffing, bool intermission,
+			    unsigned int data_len)
+{
+	unsigned int bits;
+
+	if (is_fd) {
+		if (is_eff)
+			bits = CANFD_FRAME_HEADER_EFF_BITS;
+		else
+			bits = CANFD_FRAME_HEADER_SFF_BITS;
+	} else {
+		if (is_eff)
+			bits = CAN_FRAME_HEADER_EFF_BITS;
+		else
+			bits = CAN_FRAME_HEADER_SFF_BITS;
+	}
+
+	bits += data_len * BITS_PER_BYTE;
+
+	if (!is_fd) {
+		bits += CAN_FRAME_CRC_FIELD_BITS;
+		/*
+		 * In Classical CAN, bit stuffing applies to all field
+		 * from SOF to CRC delimiter
+		 */
+		if (bitstuffing)
+			bits += can_bit_stuffing_overhead(bits);
+	} else {
+		/*
+		 * In CAN-FD, the fields preceding the CRC field have
+		 * dynamic bit stuffing; but the CRC field has fixed
+		 * bitstuffing
+		 */
+		if (bitstuffing)
+			bits += can_bit_stuffing_overhead(bits - 1);
+		if (data_len <= 16)
+			bits += CANFD_FRAME_CRC17_FIELD_BITS;
+		else
+			bits += CANFD_FRAME_CRC21_FIELD_BITS;
+	}
+
+	bits += CAN_FRAME_FOOTER_BITS;
+
+	if (intermission)
+		bits += CAN_INTERMISSION_BITS;
+
+	return bits;
+}
 
 /*
- * Size of a CAN-FD Extended Frame
- *
- * Name of Field			Bits
- * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote Request Substitution (RRS)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
+ * Number of bytes in a CAN frame
+ * (rounded up, including intermission)
  */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
+static inline
+unsigned int can_frame_bytes(bool is_fd, bool is_eff, bool bitstuffing,
+			     unsigned int data_len)
+{
+	return DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing, true,
+					   data_len),
+			    BITS_PER_BYTE);
+}
 
 /*
  * Maximum size of a Classical CAN frame
- * (rounded up and ignoring bitstuffing)
+ * (rounded up, ignoring bitstuffing but including intermission)
  */
-#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)
+#define CAN_FRAME_LEN_MAX				\
+	DIV_ROUND_UP(CAN_FRAME_HEADER_EFF_BITS +	\
+		     CAN_MAX_DLEN * BITS_PER_BYTE +	\
+		     CAN_FRAME_CRC_FIELD_BITS +		\
+		     CAN_FRAME_FOOTER_BITS +		\
+		     CAN_INTERMISSION_BITS,		\
+		     BITS_PER_BYTE)
 
 /*
  * Maximum size of a CAN-FD frame
  * (rounded up and ignoring bitstuffing)
  */
-#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)
+#define CANFD_FRAME_LEN_MAX				\
+	DIV_ROUND_UP(CANFD_FRAME_HEADER_EFF_BITS +	\
+		     CANFD_MAX_DLEN * BITS_PER_BYTE +	\
+		     CANFD_FRAME_CRC21_FIELD_BITS	\
+		     CAN_FRAME_FOOTER_BITS +		\
+		     CAN_INTERMISSION_BITS,		\
+		     BITS_PER_BYTE)
 
 /*
  * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
-- 
2.25.1

Re: [PATCH v2 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent MAILHOL]

Sorry for the late reply, I wanted to have this completed earlier but
other imperatives and the time needed to debug decided differently.

On Tue. 23 May 2023 at 15:52, Vincent Mailhol
<mailhol.vincent@wanadoo.fr> wrote:
> Introduce a method to calculate the exact size in bits of a CAN(-FD)
> frame with or without dynamic bitsuffing.
>
> These are all the possible combinations taken into account:
>
>   - Classical CAN or CAN-FD
>   - Standard or Extended frame format
>   - CAN-FD CRC17 or CRC21
>   - Include or not intermission
>
> Instead of doing several macro definitions, declare the
> can_frame_bits() static inline function. To this extend, do a full
                                                   ^^^^^^
Typo: extent
(I will not send a v3 just for that).

> refactoring of the length definitions.
>
> If given integer constant expressions as argument, can_frame_bits()
> folds into a compile time constant expression, giving no penalty over
> the use of macros.
>
> Also add the can_frame_bytes(). This function replaces the existing
> macro:
>
>   - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
>   - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
>   - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
>   - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
>
> The different frame lengths (including intermission) are as follow:
>
>    Frame type                           bits    bytes
>   ----------------------------------------------------------
>    Classic CAN SFF no-bitstuffing       111     14
>    Classic CAN EFF no-bitstuffing       131     17
>    Classic CAN SFF bitstuffing          135     17
>    Classic CAN EFF bitstuffing          160     20
>    CAN-FD SFF no-bitstuffing            579     73
>    CAN-FD EFF no-bitstuffing            598     75
>    CAN-FD SFF bitstuffing               712     89
>    CAN-FD EFF bitstuffing               736     92
>
> The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept to be
> used in const struct declarations (folding of can_frame_bytes() occurs
> too late in the compilation to be used in struct declarations).

To be fair, I am not fully happy with that part. The fact that
can_frame_bits() and can_frame_bytes() can not be used in structure
declaration even if these are compile time constants is unfortunate.
But after reflection, I still see those inline functions as a better
compromise than a collection of macro definitions. Let me know your
thoughts.

(...)

Yours sincerely,
Vincent Mailhol

Re: [PATCH v2 3/3] can: length: refactor frame lengths definition to add size in bits

[Simon Horman]

On Tue, May 23, 2023 at 03:52:18PM +0900, Vincent Mailhol wrote:
> Introduce a method to calculate the exact size in bits of a CAN(-FD)
> frame with or without dynamic bitsuffing.

...

> +/**
> + * can_frame_bits() - Calculate the number of bits in on the wire in a
> + *	CAN frame

nit: @is_fd should be documented here.

> + * @is_eff: true: Extended Frame; false: Standard Frame.
> + * @bitstuffing: if true, calculate the bitsuffing worst case, if
> + *	false, calculated the bitsuffing best case (no dynamic
> + *	bitsuffing). Fixed stuff bits always get included.
> + * @intermission: if and only if true, include the inter frame space
> + *	assuming no bus idle (i.e. only the intermission gets added).
> + * @data_len: length of the data field in bytes. Correspond to
> + *	can(fd)_frame->len. Should be zero for remote frames. No
> + *	sanitization is done on @data_len.
> + *
> + * Return: the numbers of bits on the wire of a CAN frame.
> + */
> +static inline
> +unsigned int can_frame_bits(bool is_fd, bool is_eff,
> +			    bool bitstuffing, bool intermission,
> +			    unsigned int data_len)
> +{

...

[PATCH v3 0/3] can: length: fix definitions and add bit length calculation

[Vincent Mailhol]

When created in [1], frames length definitions were added to implement
byte queue limits (bql). Because bql expects lengths in bytes, bit
length definitions were not considered back then.
    
Recently, a need to refer to the exact frame length in bits, with CAN
bit stuffing, appeared in [2].

This series introduces can_frame_bits(): a function-like macro that
can calculate the exact size of a CAN(-FD) frame in bits with or
without bitsuffing.

[1] commit 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce
    function to get data length of frame in data link layer")
Link: https://git.kernel.org/torvalds/c/85d99c3e2a13

[2] RE: [PATCH] can: mcp251xfd: Increase poll timeout
Link: https://lore.kernel.org/linux-can/BL3PR11MB64846C83ACD04E9330B0FE66FB729@BL3PR11MB6484.namprd11.prod.outlook.com/


* Changelog *

v2 -> v3:

  * turn can_frame_bits() and can_frame_bytes() into function-like
    macros. The fact that inline functions can not be used to
    initialize constant structure fields was bothering me. I did my
    best to make the macro look as less ugly as possible.

  * as reported by Simon Horman, add missing document for the is_fd
    argument of can_frame_bits().

Link: https://lore.kernel.org/linux-can/20230523065218.51227-1-mailhol.vincent@wanadoo.fr/

v1 -> v2:

  * as suggested by Thomas Kopp, add a new patch to the series to fix
    the stuff bit count and the fixed stuff bits definitions

  * and another patch to fix documentation of the Remote Request
    Substitution (RRS).

  * refactor the length definition. Instead of using individual macro,
    rely on an inline function. One reason is to minimize the number
    of definitions. An other reason is that because the dynamic bit
    stuff is calculated differently for CAN and CAN-FD, it is just not
    possible to multiply the existing CANFD_FRAME_OVERHEAD_SFF/EFF by
    the overhead ratio to get the bitsuffing: for CAN-FD, the CRC
    field is already stuffed by the fix stuff bits and is out of scope
    of the dynamic bitstuffing.

Link: https://lore.kernel.org/linux-can/20230507155506.3179711-1-mailhol.vincent@wanadoo.fr/

Vincent Mailhol (3):
  can: length: fix bitstuffing count
  can: length: fix description of the RRS field
  can: length: refactor frame lengths definition to add size in bits

 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 295 +++++++++++++++++++++++++----------
 2 files changed, 213 insertions(+), 97 deletions(-)

-- 
2.39.3

[PATCH v3 1/3] can: length: fix bitstuffing count

[Vincent Mailhol]

The Stuff Bit Count is always coded on 4 bits (ref [1]). Update the
Stuff Bit Count size accordingly.

In addition, the CRC fields of CAN FD Frames contain stuff bits at
fixed positions called fixed stuff bits [2]. The CRC field starts with
a fixed stuff bit and then has another fixed stuff bit after each
fourth bit [2], which allows us to derive this formula:

  FSB count = 1 + round_down(len(CRC field)/4)

The length of the CRC field is [1]:

  len(CRC field) = len(Stuff Bit Count) + len(CRC)
                 = 4 + len(CRC)

with len(CRC) either 17 or 21 bits depending of the payload length.

In conclusion, for CRC17:

  FSB count = 1 + round_down((4 + 17)/4)
            = 6

and for CRC 21:

  FSB count = 1 + round_down((4 + 21)/4)
            = 7

Add a Fixed Stuff bits (FSB) field with above values and update
CANFD_FRAME_OVERHEAD_SFF and CANFD_FRAME_OVERHEAD_EFF accordingly.

[1] ISO 11898-1:2015 section 10.4.2.6 "CRC field":

  The CRC field shall contain the CRC sequence followed by a recessive
  CRC delimiter. For FD Frames, the CRC field shall also contain the
  stuff count.

  Stuff count

  If FD Frames, the stuff count shall be at the beginning of the CRC
  field. It shall consist of the stuff bit count modulo 8 in a 3-bit
  gray code followed by a parity bit [...]

[2] ISO 11898-1:2015 paragraph 10.5 "Frame coding":

  In the CRC field of FD Frames, the stuff bits shall be inserted at
  fixed positions; they are called field stuff bits. There shall be a
  fixed stuff bit before the first bit of the stuff count, even if the
  last bits of the preceding field are a sequence of five consecutive
  bits of identical value, there shall be only the fixed stuff bit,
  there shall not be two consecutive stuff bits. A further fixed stuff
  bit shall be inserted after each fourth bit of the CRC field [...]

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 include/linux/can/length.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 69336549d24f..b8c12c83bc51 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -72,17 +72,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
+#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
 
 /*
  * Size of a CAN-FD Extended Frame
@@ -101,17 +102,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
+#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
 
 /*
  * Maximum size of a Classical CAN frame
-- 
2.39.3

[PATCH v3 2/3] can: length: fix description of the RRS field

[Vincent Mailhol]

The CAN-FD frames only have one reserved bit. The bit corresponding to
Classical CAN frame's RTR bit is called the "Remote Request
Substitution (RRS)" [1].

N.B. The RRS is not to be confused with the Substitute remote request
(SRR).

Fix the description in the CANFD_FRAME_OVERHEAD_SFF/EFF.

The total remains unchanged, so this is just a documentation fix.

In addition to the above add myself as copyright owner for 2020 (as
coauthor of the initial version, c.f. Fixes tag).

[1] ISO 11898-1:2015 paragraph 10.4.2.3 "Arbitration field":

  RSS bit [only in FD Frames]

    The RRS bit shall be transmitted in fD Frames at the position of
    the RTR bit in Classical Frames. The RRS bit shall be transmitted
    dominant, but receivers shall accept recessive and dominant RRS
    bits.

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 include/linux/can/length.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index b8c12c83bc51..521fdbce2d69 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
+ * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
@@ -64,7 +65,7 @@
  * ---------------------------------------------------------
  * Start-of-frame			1
  * Identifier				11
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Identifier extension bit (IDE)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
@@ -95,7 +96,7 @@
  * Substitute remote request (SRR)	1
  * Identifier extension bit (IDE)	1
  * Identifier B				18
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
  * Bit Rate Switch (BRS)		1
-- 
2.39.3

[PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent Mailhol]

Introduce a method to calculate the exact size in bits of a CAN(-FD)
frame with or without dynamic bitsuffing.

These are all the possible combinations taken into account:

  - Classical CAN or CAN-FD
  - Standard or Extended frame format
  - CAN-FD CRC17 or CRC21
  - Include or not intermission

Instead of doing several individual macro definitions, declare the
can_frame_bits() function-like macro. To this extent, do a full
refactoring of the length definitions.

In addition add the can_frame_bytes(). This function-like macro
replaces the existing macro:

  - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
  - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
  - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
  - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)

The different maximum frame lengths (maximum data length, including
intermission) are as follow:

   Frame type				bits	bytes
  -------------------------------------------------------
   Classic CAN SFF no-bitstuffing	111	14
   Classic CAN EFF no-bitstuffing	131	17
   Classic CAN SFF bitstuffing		135	17
   Classic CAN EFF bitstuffing		160	20
   CAN-FD SFF no-bitstuffing		579	73
   CAN-FD EFF no-bitstuffing		598	75
   CAN-FD SFF bitstuffing		712	89
   CAN-FD EFF bitstuffing		736	92

The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
can_frame_bytes(true, true, CANFD_MAX_DLEN).

In addition to the above:

 - Use ISO 11898-1:2015 definitions for the name of the CAN frame
   fields.
 - Include linux/bits.h for use of BITS_PER_BYTE.
 - Include linux/math.h for use of mult_frac() and
   DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
   patch, but the include was previously omitted.
 - Add copyright 2023 for myself.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 298 +++++++++++++++++++++++++----------
 2 files changed, 213 insertions(+), 100 deletions(-)

diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
index b48140b1102e..b7f4d76dd444 100644
--- a/drivers/net/can/dev/length.c
+++ b/drivers/net/can/dev/length.c
@@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
 	else
 		len = cf->len;
 
-	if (can_is_canfd_skb(skb)) {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CANFD_FRAME_OVERHEAD_EFF;
-		else
-			len += CANFD_FRAME_OVERHEAD_SFF;
-	} else {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CAN_FRAME_OVERHEAD_EFF;
-		else
-			len += CAN_FRAME_OVERHEAD_SFF;
-	}
-
-	return len;
+	return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,
+			       false, len);
 }
 EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 521fdbce2d69..ef6e78fa95b9 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,132 +1,256 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
- * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
+ * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
 #define _CAN_LENGTH_H
 
+#include <linux/bits.h>
 #include <linux/can.h>
 #include <linux/can/netlink.h>
+#include <linux/math.h>
 
 /*
- * Size of a Classical CAN Standard Frame
+ * Size of a Classical CAN Standard Frame header in bits
  *
- * Name of Field			Bits
+ * Name of Field				Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote transmission request (RTR)	1
- * Identifier extension bit (IDE)	1
- * Reserved bit (r0)			1
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicatior (FDF)		1
+ *	Data Length Code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CAN_FRAME_HEADER_SFF_BITS 19
+
+/*
+ * Size of a Classical CAN Extended Frame header in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	FD Format indicatior (FDF)		1
+ *	Reserved bit (r0)			1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CAN_FRAME_HEADER_EFF_BITS 39
+
+/*
+ * Size of a CAN-FD Standard Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_SFF_BITS 22
+
+/*
+ * Size of a CAN-FD Extended Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
  *
- * rounded up and ignoring bitstuffing
+ * including all fields preceding the data field, ignoring bitstuffing
  */
-#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+#define CANFD_FRAME_HEADER_EFF_BITS 41
 
 /*
- * Size of a Classical CAN Extended Frame
+ * Size of a CAN CRC Field in bits
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote transmission request (RTR)	1
- * Reserved bits (r1, r0)		2
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * CRC sequence (CRC15)			15
+ * CRC Delimiter			1
  *
- * rounded up and ignoring bitstuffing
+ * ignoring bitstuffing
  */
-#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+#define CAN_FRAME_CRC_FIELD_BITS 16
 
 /*
- * Size of a CAN-FD Standard Frame
+ * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote Request Substitution (RRS)	1
- * Identifier extension bit (IDE)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
- */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
+ * Stuff Count				4
+ * CRC Sequence (CRC17)			17
+ * CRC Delimiter			1
+ * Fixed stuff bits			6
+ */
+#define CANFD_FRAME_CRC17_FIELD_BITS 28
 
 /*
- * Size of a CAN-FD Extended Frame
+ * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote Request Substitution (RRS)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
- */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
+ * Stuff Count				4
+ * CRC sequence (CRC21)			21
+ * CRC Delimiter			1
+ * Fixed stuff bits			7
+ */
+#define CANFD_FRAME_CRC21_FIELD_BITS 33
+
+/*
+ * Size of a CAN(-FD) Frame footer in bits
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * ACK slot				1
+ * ACK delimiter			1
+ * End Of Frame (EOF)			7
+ *
+ * including all fields following the CRC field
+ */
+#define CAN_FRAME_FOOTER_BITS 9
+
+/*
+ * First part of the Inter Frame Space
+ * (a.k.a. IMF - intermission field)
+ */
+#define CAN_INTERMISSION_BITS 3
+
+/**
+ * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
+ * @bitstream_len: length of a destuffed bit stream
+ *
+ * The worst bit stuffing case is a sequence in which dominant and
+ * recessive bits alternate every four bits:
+ *
+ *   Destuffed: 1 1111  0000  1111  0000  1111
+ *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
+ *
+ * Nomenclature
+ *
+ *  - "0": dominant bit
+ *  - "o": dominant stuff bit
+ *  - "1": recessive bit
+ *  - "i": recessive stuff bit
+ *
+ * Aside of the first bit, one stuff bit is added every four bits.
+ *
+ * Return: length of the stuffed bit stream in the worst case scenario.
+ */
+#define can_bitstuffing_len(destuffed_len)			\
+	(destuffed_len + (destuffed_len - 1) / 4)
+
+#define __can_bitstuffing_len(bitstuffing, destuffed_len)	\
+	(bitstuffing ? can_bitstuffing_len(destuffed_len) :	\
+		       destuffed_len)
+
+#define __can_cc_frame_bits(is_eff, bitstuffing,		\
+			    intermission, data_len)		\
+(								\
+	__can_bitstuffing_len(bitstuffing,			\
+		(is_eff ? CAN_FRAME_HEADER_EFF_BITS :		\
+			   CAN_FRAME_HEADER_SFF_BITS) +		\
+		data_len * BITS_PER_BYTE +			\
+		CAN_FRAME_CRC_FIELD_BITS) +			\
+	CAN_FRAME_FOOTER_BITS +					\
+	(intermission ? CAN_INTERMISSION_BITS : 0)		\
+)
+
+#define __can_fd_frame_bits(is_eff, bitstuffing,		\
+			    intermission, data_len)		\
+(								\
+	__can_bitstuffing_len(bitstuffing,			\
+		(is_eff ? CANFD_FRAME_HEADER_EFF_BITS :		\
+			   CANFD_FRAME_HEADER_SFF_BITS) +	\
+		data_len * BITS_PER_BYTE) +			\
+	(data_len <= 16 ?					\
+		CANFD_FRAME_CRC17_FIELD_BITS :			\
+		CANFD_FRAME_CRC21_FIELD_BITS) +			\
+	CAN_FRAME_FOOTER_BITS +					\
+	(intermission ? CAN_INTERMISSION_BITS : 0)		\
+)
+
+/**
+ * can_frame_bits() - Calculate the number of bits in on the wire in a
+ *	CAN frame
+ * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
+ * @is_eff: true: Extended frame; false: Standard frame.
+ * @bitstuffing: true: calculate the bitsuffing worst case; false:
+ *	calculate the bitsuffing best case (no dynamic
+ *	bitsuffing). Fixed stuff bits are always included.
+ * @intermission: if and only if true, include the inter frame space
+ *	assuming no bus idle (i.e. only the intermission gets added).
+ * @data_len: length of the data field in bytes. Correspond to
+ *	can(fd)_frame->len. Should be zero for remote frames. No
+ *	sanitization is done on @data_len.
+ *
+ * Return: the numbers of bits on the wire of a CAN frame.
+ */
+#define can_frame_bits(is_fd, is_eff, bitstuffing,		\
+		       intermission, data_len)			\
+(								\
+	is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,	\
+				    intermission, data_len) :	\
+		__can_cc_frame_bits(is_eff, bitstuffing,	\
+				    intermission, data_len)	\
+)
+
+/*
+ * Number of bytes in a CAN frame
+ * (rounded up, including intermission)
+ */
+#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)	\
+	DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing,	\
+				    true, data_len),		\
+		     BITS_PER_BYTE)
 
 /*
  * Maximum size of a Classical CAN frame
- * (rounded up and ignoring bitstuffing)
+ * (rounded up, ignoring bitstuffing but including intermission)
  */
-#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)
+#define CAN_FRAME_LEN_MAX \
+	can_frame_bytes(false, true, false, CAN_MAX_DLEN)
 
 /*
  * Maximum size of a CAN-FD frame
  * (rounded up and ignoring bitstuffing)
  */
-#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)
+#define CANFD_FRAME_LEN_MAX \
+	can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
 
 /*
  * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
-- 
2.39.3

Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Simon Horman]

On Tue, May 30, 2023 at 11:46:37PM +0900, Vincent Mailhol wrote:
> Introduce a method to calculate the exact size in bits of a CAN(-FD)
> frame with or without dynamic bitsuffing.
> 
> These are all the possible combinations taken into account:
> 
>   - Classical CAN or CAN-FD
>   - Standard or Extended frame format
>   - CAN-FD CRC17 or CRC21
>   - Include or not intermission
> 
> Instead of doing several individual macro definitions, declare the
> can_frame_bits() function-like macro. To this extent, do a full
> refactoring of the length definitions.
> 
> In addition add the can_frame_bytes(). This function-like macro
> replaces the existing macro:
> 
>   - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
>   - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
>   - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
>   - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
> 
> The different maximum frame lengths (maximum data length, including
> intermission) are as follow:
> 
>    Frame type				bits	bytes
>   -------------------------------------------------------
>    Classic CAN SFF no-bitstuffing	111	14
>    Classic CAN EFF no-bitstuffing	131	17
>    Classic CAN SFF bitstuffing		135	17
>    Classic CAN EFF bitstuffing		160	20
>    CAN-FD SFF no-bitstuffing		579	73
>    CAN-FD EFF no-bitstuffing		598	75
>    CAN-FD SFF bitstuffing		712	89
>    CAN-FD EFF bitstuffing		736	92
> 
> The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
> alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
> can_frame_bytes(true, true, CANFD_MAX_DLEN).
> 
> In addition to the above:
> 
>  - Use ISO 11898-1:2015 definitions for the name of the CAN frame
>    fields.
>  - Include linux/bits.h for use of BITS_PER_BYTE.
>  - Include linux/math.h for use of mult_frac() and
>    DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
>    patch, but the include was previously omitted.
>  - Add copyright 2023 for myself.
> 
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

...

> +/**
> + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
> + * @bitstream_len: length of a destuffed bit stream

Hi Vincent,

it looks like an editing error has crept in here:

	s/bitstream_len/destuffed_len/

> + *
> + * The worst bit stuffing case is a sequence in which dominant and
> + * recessive bits alternate every four bits:
> + *
> + *   Destuffed: 1 1111  0000  1111  0000  1111
> + *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
> + *
> + * Nomenclature
> + *
> + *  - "0": dominant bit
> + *  - "o": dominant stuff bit
> + *  - "1": recessive bit
> + *  - "i": recessive stuff bit
> + *
> + * Aside of the first bit, one stuff bit is added every four bits.
> + *
> + * Return: length of the stuffed bit stream in the worst case scenario.
> + */
> +#define can_bitstuffing_len(destuffed_len)			\
> +	(destuffed_len + (destuffed_len - 1) / 4)

Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent MAILHOL]

On Wed. 31 May 2023 at 00:56, Simon Horman <simon.horman@corigine.com> wrote:
> On Tue, May 30, 2023 at 11:46:37PM +0900, Vincent Mailhol wrote:
> > Introduce a method to calculate the exact size in bits of a CAN(-FD)
> > frame with or without dynamic bitsuffing.
> >
> > These are all the possible combinations taken into account:
> >
> >   - Classical CAN or CAN-FD
> >   - Standard or Extended frame format
> >   - CAN-FD CRC17 or CRC21
> >   - Include or not intermission
> >
> > Instead of doing several individual macro definitions, declare the
> > can_frame_bits() function-like macro. To this extent, do a full
> > refactoring of the length definitions.
> >
> > In addition add the can_frame_bytes(). This function-like macro
> > replaces the existing macro:
> >
> >   - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
> >   - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
> >   - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
> >   - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
> >
> > The different maximum frame lengths (maximum data length, including
> > intermission) are as follow:
> >
> >    Frame type                         bits    bytes
> >   -------------------------------------------------------
> >    Classic CAN SFF no-bitstuffing     111     14
> >    Classic CAN EFF no-bitstuffing     131     17
> >    Classic CAN SFF bitstuffing                135     17
> >    Classic CAN EFF bitstuffing                160     20
> >    CAN-FD SFF no-bitstuffing          579     73
> >    CAN-FD EFF no-bitstuffing          598     75
> >    CAN-FD SFF bitstuffing             712     89
> >    CAN-FD EFF bitstuffing             736     92
> >
> > The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
> > alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
> > can_frame_bytes(true, true, CANFD_MAX_DLEN).
> >
> > In addition to the above:
> >
> >  - Use ISO 11898-1:2015 definitions for the name of the CAN frame
> >    fields.
> >  - Include linux/bits.h for use of BITS_PER_BYTE.
> >  - Include linux/math.h for use of mult_frac() and
> >    DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
> >    patch, but the include was previously omitted.
> >  - Add copyright 2023 for myself.
> >
> > Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
>
> ...
>
> > +/**
> > + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
> > + * @bitstream_len: length of a destuffed bit stream
>
> Hi Vincent,
>
> it looks like an editing error has crept in here:
>
>         s/bitstream_len/destuffed_len/

Doh! Thanks for picking this up.

I already prepared a v4 locally. Before sending it, I will wait one
day to see if there are other comments.

> > + *
> > + * The worst bit stuffing case is a sequence in which dominant and
> > + * recessive bits alternate every four bits:
> > + *
> > + *   Destuffed: 1 1111  0000  1111  0000  1111
> > + *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
> > + *
> > + * Nomenclature
> > + *
> > + *  - "0": dominant bit
> > + *  - "o": dominant stuff bit
> > + *  - "1": recessive bit
> > + *  - "i": recessive stuff bit
> > + *
> > + * Aside of the first bit, one stuff bit is added every four bits.
> > + *
> > + * Return: length of the stuffed bit stream in the worst case scenario.
> > + */
> > +#define can_bitstuffing_len(destuffed_len)                   \
> > +     (destuffed_len + (destuffed_len - 1) / 4)

Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Simon Horman]

On Wed, May 31, 2023 at 02:29:43AM +0900, Vincent MAILHOL wrote:
> On Wed. 31 May 2023 at 00:56, Simon Horman <simon.horman@corigine.com> wrote:
> > On Tue, May 30, 2023 at 11:46:37PM +0900, Vincent Mailhol wrote:

...

> > > +/**
> > > + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
> > > + * @bitstream_len: length of a destuffed bit stream
> >
> > Hi Vincent,
> >
> > it looks like an editing error has crept in here:
> >
> >         s/bitstream_len/destuffed_len/
> 
> Doh! Thanks for picking this up.
> 
> I already prepared a v4 locally. Before sending it, I will wait one
> day to see if there are other comments.

Thanks, sounds good.

-- 
pw-bot: cr

Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent MAILHOL]

On Wed. 31 May 2023 at 04:53, Simon Horman <simon.horman@corigine.com> wrote:
> On Wed, May 31, 2023 at 02:29:43AM +0900, Vincent MAILHOL wrote:
> > On Wed. 31 May 2023 at 00:56, Simon Horman <simon.horman@corigine.com> wrote:
> > > On Tue, May 30, 2023 at 11:46:37PM +0900, Vincent Mailhol wrote:
>
> ...
>
> > > > +/**
> > > > + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
> > > > + * @bitstream_len: length of a destuffed bit stream
> > >
> > > Hi Vincent,
> > >
> > > it looks like an editing error has crept in here:
> > >
> > >         s/bitstream_len/destuffed_len/
> >
> > Doh! Thanks for picking this up.
> >
> > I already prepared a v4 locally. Before sending it, I will wait one
> > day to see if there are other comments.
>
> Thanks, sounds good.

On a side note, I was puzzled because I did not get any documentation
warnings when running a "make W=1". I just realized that only .c files
get checked, not headers. I sent a separate patch to fix the
documentation:

  https://lore.kernel.org/linux-doc/20230531093951.358769-1-mailhol.vincent@wanadoo.fr/

Yours sincerely,
Vincent Mailhol

RE: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Thomas.Kopp]

> Introduce a method to calculate the exact size in bits of a CAN(-FD)
> frame with or without dynamic bitsuffing.
> 
> These are all the possible combinations taken into account:
> 
>   - Classical CAN or CAN-FD
>   - Standard or Extended frame format
>   - CAN-FD CRC17 or CRC21
>   - Include or not intermission
> 
> Instead of doing several individual macro definitions, declare the
> can_frame_bits() function-like macro. To this extent, do a full
> refactoring of the length definitions.
> 
> In addition add the can_frame_bytes(). This function-like macro
> replaces the existing macro:
> 
>   - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
>   - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
>   - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
>   - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
> 
> The different maximum frame lengths (maximum data length, including
> intermission) are as follow:
> 
>    Frame type                           bits    bytes
>   -------------------------------------------------------
>    Classic CAN SFF no-bitstuffing       111     14
>    Classic CAN EFF no-bitstuffing       131     17
>    Classic CAN SFF bitstuffing          135     17
>    Classic CAN EFF bitstuffing          160     20
>    CAN-FD SFF no-bitstuffing            579     73
>    CAN-FD EFF no-bitstuffing            598     75
>    CAN-FD SFF bitstuffing               712     89
>    CAN-FD EFF bitstuffing               736     92
> 
> The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as
> an
> alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
> can_frame_bytes(true, true, CANFD_MAX_DLEN).
> 
> In addition to the above:
> 
>  - Use ISO 11898-1:2015 definitions for the name of the CAN frame
>    fields.
>  - Include linux/bits.h for use of BITS_PER_BYTE.
>  - Include linux/math.h for use of mult_frac() and
>    DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
>    patch, but the include was previously omitted.
>  - Add copyright 2023 for myself.
> 
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> ---
>  drivers/net/can/dev/length.c |  15 +-
>  include/linux/can/length.h   | 298 +++++++++++++++++++++++++----------
>  2 files changed, 213 insertions(+), 100 deletions(-)
> 
> diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
> index b48140b1102e..b7f4d76dd444 100644
> --- a/drivers/net/can/dev/length.c
> +++ b/drivers/net/can/dev/length.c
> @@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct
> sk_buff *skb)
>         else
>                 len = cf->len;
> 
> -       if (can_is_canfd_skb(skb)) {
> -               if (cf->can_id & CAN_EFF_FLAG)
> -                       len += CANFD_FRAME_OVERHEAD_EFF;
> -               else
> -                       len += CANFD_FRAME_OVERHEAD_SFF;
> -       } else {
> -               if (cf->can_id & CAN_EFF_FLAG)
> -                       len += CAN_FRAME_OVERHEAD_EFF;
> -               else
> -                       len += CAN_FRAME_OVERHEAD_SFF;
> -       }
> -
> -       return len;
> +       return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id &
> CAN_EFF_FLAG,
> +                              false, len);
>  }
>  EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
> diff --git a/include/linux/can/length.h b/include/linux/can/length.h
> index 521fdbce2d69..ef6e78fa95b9 100644
> --- a/include/linux/can/length.h
> +++ b/include/linux/can/length.h
> @@ -1,132 +1,256 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
>  /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
>   * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
> - * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> + * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
>   */
> 
>  #ifndef _CAN_LENGTH_H
>  #define _CAN_LENGTH_H
> 
> +#include <linux/bits.h>
>  #include <linux/can.h>
>  #include <linux/can/netlink.h>
> +#include <linux/math.h>
> 
>  /*
> - * Size of a Classical CAN Standard Frame
> + * Size of a Classical CAN Standard Frame header in bits
>   *
> - * Name of Field                       Bits
> + * Name of Field                               Bits
>   * ---------------------------------------------------------
> - * Start-of-frame                      1
> - * Identifier                          11
> - * Remote transmission request (RTR)   1
> - * Identifier extension bit (IDE)      1
> - * Reserved bit (r0)                   1
> - * Data length code (DLC)              4
> - * Data field                          0...64
> - * CRC                                 15
> - * CRC delimiter                       1
> - * ACK slot                            1
> - * ACK delimiter                       1
> - * End-of-frame (EOF)                  7
> - * Inter frame spacing                 3
> + * Start Of Frame (SOF)                                1
> + * Arbitration field:
> + *     base ID                                 11
> + *     Remote Transmission Request (RTR)       1
> + * Control field:
> + *     IDentifier Extension bit (IDE)          1
> + *     FD Format indicatior (FDF)              1
> + *     Data Length Code (DLC)                  4
> + *
> + * including all fields preceding the data field, ignoring bitstuffing
> + */
> +#define CAN_FRAME_HEADER_SFF_BITS 19
> +
> +/*
> + * Size of a Classical CAN Extended Frame header in bits
> + *
> + * Name of Field                               Bits
> + * ---------------------------------------------------------
> + * Start Of Frame (SOF)                                1
> + * Arbitration field:
> + *     base ID                                 11
> + *     Substitute Remote Request (SRR)         1
> + *     IDentifier Extension bit (IDE)          1
> + *     ID extension                            18
> + *     Remote Transmission Request (RTR)       1
> + * Control field:
> + *     FD Format indicatior (FDF)              1
Nit: indicator, same above
> + *     Reserved bit (r0)                       1
> + *     Data length code (DLC)                  4
> + *
> + * including all fields preceding the data field, ignoring bitstuffing
> + */
> +#define CAN_FRAME_HEADER_EFF_BITS 39
> +
> +/*
> + * Size of a CAN-FD Standard Frame in bits
> + *
> + * Name of Field                               Bits
> + * ---------------------------------------------------------
> + * Start Of Frame (SOF)                                1
> + * Arbitration field:
> + *     base ID                                 11
> + *     Remote Request Substitution (RRS)       1
> + * Control field:
> + *     IDentifier Extension bit (IDE)          1
> + *     FD Format indicator (FDF)               1
> + *     Reserved bit (res)                      1
> + *     Bit Rate Switch (BRS)                   1
> + *     Error Status Indicator (ESI)            1
> + *     Data length code (DLC)                  4
> + *
> + * including all fields preceding the data field, ignoring bitstuffing
> + */
> +#define CANFD_FRAME_HEADER_SFF_BITS 22
> +
> +/*
> + * Size of a CAN-FD Extended Frame in bits
> + *
> + * Name of Field                               Bits
> + * ---------------------------------------------------------
> + * Start Of Frame (SOF)                                1
> + * Arbitration field:
> + *     base ID                                 11
> + *     Substitute Remote Request (SRR)         1
> + *     IDentifier Extension bit (IDE)          1
> + *     ID extension                            18
> + *     Remote Request Substitution (RRS)       1
> + * Control field:
> + *     FD Format indicator (FDF)               1
> + *     Reserved bit (res)                      1
> + *     Bit Rate Switch (BRS)                   1
> + *     Error Status Indicator (ESI)            1
> + *     Data length code (DLC)                  4
>   *
> - * rounded up and ignoring bitstuffing
> + * including all fields preceding the data field, ignoring bitstuffing
>   */
> -#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
> +#define CANFD_FRAME_HEADER_EFF_BITS 41
> 
>  /*
> - * Size of a Classical CAN Extended Frame
> + * Size of a CAN CRC Field in bits
>   *
>   * Name of Field                       Bits
>   * ---------------------------------------------------------
> - * Start-of-frame                      1
> - * Identifier A                                11
> - * Substitute remote request (SRR)     1
> - * Identifier extension bit (IDE)      1
> - * Identifier B                                18
> - * Remote transmission request (RTR)   1
> - * Reserved bits (r1, r0)              2
> - * Data length code (DLC)              4
> - * Data field                          0...64
> - * CRC                                 15
> - * CRC delimiter                       1
> - * ACK slot                            1
> - * ACK delimiter                       1
> - * End-of-frame (EOF)                  7
> - * Inter frame spacing                 3
> + * CRC sequence (CRC15)                        15
> + * CRC Delimiter                       1
>   *
> - * rounded up and ignoring bitstuffing
> + * ignoring bitstuffing
>   */
> -#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
> +#define CAN_FRAME_CRC_FIELD_BITS 16
> 
>  /*
> - * Size of a CAN-FD Standard Frame
> + * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
>   *
>   * Name of Field                       Bits
>   * ---------------------------------------------------------
> - * Start-of-frame                      1
> - * Identifier                          11
> - * Remote Request Substitution (RRS)   1
> - * Identifier extension bit (IDE)      1
> - * Flexible data rate format (FDF)     1
> - * Reserved bit (r0)                   1
> - * Bit Rate Switch (BRS)               1
> - * Error Status Indicator (ESI)                1
> - * Data length code (DLC)              4
> - * Data field                          0...512
> - * Stuff Bit Count (SBC)               4
> - * CRC                                 0...16: 17 20...64:21
> - * CRC delimiter (CD)                  1
> - * Fixed Stuff bits (FSB)              0...16: 6 20...64:7
> - * ACK slot (AS)                       1
> - * ACK delimiter (AD)                  1
> - * End-of-frame (EOF)                  7
> - * Inter frame spacing                 3
> - *
> - * assuming CRC21, rounded up and ignoring dynamic bitstuffing
> - */
> -#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
> + * Stuff Count                         4
> + * CRC Sequence (CRC17)                        17
> + * CRC Delimiter                       1
> + * Fixed stuff bits                    6
> + */
> +#define CANFD_FRAME_CRC17_FIELD_BITS 28
> 
>  /*
> - * Size of a CAN-FD Extended Frame
> + * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
>   *
>   * Name of Field                       Bits
>   * ---------------------------------------------------------
> - * Start-of-frame                      1
> - * Identifier A                                11
> - * Substitute remote request (SRR)     1
> - * Identifier extension bit (IDE)      1
> - * Identifier B                                18
> - * Remote Request Substitution (RRS)   1
> - * Flexible data rate format (FDF)     1
> - * Reserved bit (r0)                   1
> - * Bit Rate Switch (BRS)               1
> - * Error Status Indicator (ESI)                1
> - * Data length code (DLC)              4
> - * Data field                          0...512
> - * Stuff Bit Count (SBC)               4
> - * CRC                                 0...16: 17 20...64:21
> - * CRC delimiter (CD)                  1
> - * Fixed Stuff bits (FSB)              0...16: 6 20...64:7
> - * ACK slot (AS)                       1
> - * ACK delimiter (AD)                  1
> - * End-of-frame (EOF)                  7
> - * Inter frame spacing                 3
> - *
> - * assuming CRC21, rounded up and ignoring dynamic bitstuffing
> - */
> -#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
> + * Stuff Count                         4
> + * CRC sequence (CRC21)                        21
> + * CRC Delimiter                       1
> + * Fixed stuff bits                    7
> + */
> +#define CANFD_FRAME_CRC21_FIELD_BITS 33
> +
> +/*
> + * Size of a CAN(-FD) Frame footer in bits
> + *
> + * Name of Field                       Bits
> + * ---------------------------------------------------------
> + * ACK slot                            1
> + * ACK delimiter                       1
> + * End Of Frame (EOF)                  7
> + *
> + * including all fields following the CRC field
> + */
> +#define CAN_FRAME_FOOTER_BITS 9
> +
> +/*
> + * First part of the Inter Frame Space
> + * (a.k.a. IMF - intermission field)
> + */
> +#define CAN_INTERMISSION_BITS 3
> +
> +/**
> + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
Nit: bitstuffing, same further down
> + * @bitstream_len: length of a destuffed bit stream
> + *
> + * The worst bit stuffing case is a sequence in which dominant and
> + * recessive bits alternate every four bits:
> + *
> + *   Destuffed: 1 1111  0000  1111  0000  1111
> + *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
> + *
> + * Nomenclature
> + *
> + *  - "0": dominant bit
> + *  - "o": dominant stuff bit
> + *  - "1": recessive bit
> + *  - "i": recessive stuff bit
> + *
> + * Aside of the first bit, one stuff bit is added every four bits.
> + *
> + * Return: length of the stuffed bit stream in the worst case scenario.
> + */
> +#define can_bitstuffing_len(destuffed_len)                     \
> +       (destuffed_len + (destuffed_len - 1) / 4)
> +
> +#define __can_bitstuffing_len(bitstuffing, destuffed_len)      \
> +       (bitstuffing ? can_bitstuffing_len(destuffed_len) :     \
> +                      destuffed_len)
> +
> +#define __can_cc_frame_bits(is_eff, bitstuffing,               \
> +                           intermission, data_len)             \
> +(                                                              \
> +       __can_bitstuffing_len(bitstuffing,                      \
> +               (is_eff ? CAN_FRAME_HEADER_EFF_BITS :           \
> +                          CAN_FRAME_HEADER_SFF_BITS) +         \
> +               data_len * BITS_PER_BYTE +                      \
> +               CAN_FRAME_CRC_FIELD_BITS) +                     \
> +       CAN_FRAME_FOOTER_BITS +                                 \
> +       (intermission ? CAN_INTERMISSION_BITS : 0)              \
> +)
I think Footer and Intermission need to be pulled out of the parameter for __can_bitstuffing_length as these fields are never stuffed.
> +
> +#define __can_fd_frame_bits(is_eff, bitstuffing,               \
> +                           intermission, data_len)             \
> +(                                                              \
> +       __can_bitstuffing_len(bitstuffing,                      \
> +               (is_eff ? CANFD_FRAME_HEADER_EFF_BITS :         \
> +                          CANFD_FRAME_HEADER_SFF_BITS) +       \
> +               data_len * BITS_PER_BYTE) +                     \
> +       (data_len <= 16 ?                                       \
> +               CANFD_FRAME_CRC17_FIELD_BITS :                  \
> +               CANFD_FRAME_CRC21_FIELD_BITS) +                 \
> +       CAN_FRAME_FOOTER_BITS +                                 \
> +       (intermission ? CAN_INTERMISSION_BITS : 0)              \
> +)
I think Footer and Intermission need to be pulled out of the parameter for __can_bitstuffing_length as these fields are never stuffed.
The CAN_FRAME_CRC_FIELD_BITS bits need to be pulled out of the can_bitstuffing_len. That portion of the Frame is not dynamically stuffed in FD frames.
> +
> +/**
> + * can_frame_bits() - Calculate the number of bits in on the wire in a
Nit: "in on the wire" -in
> + *     CAN frame
> + * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
> + * @is_eff: true: Extended frame; false: Standard frame.
> + * @bitstuffing: true: calculate the bitsuffing worst case; false:
> + *     calculate the bitsuffing best case (no dynamic
> + *     bitsuffing). Fixed stuff bits are always included.
> + * @intermission: if and only if true, include the inter frame space
> + *     assuming no bus idle (i.e. only the intermission gets added).
> + * @data_len: length of the data field in bytes. Correspond to
> + *     can(fd)_frame->len. Should be zero for remote frames. No
> + *     sanitization is done on @data_len.
> + *
> + * Return: the numbers of bits on the wire of a CAN frame.
> + */
> +#define can_frame_bits(is_fd, is_eff, bitstuffing,             \
> +                      intermission, data_len)                  \
> +(                                                              \
> +       is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,        \
> +                                   intermission, data_len) :   \
> +               __can_cc_frame_bits(is_eff, bitstuffing,        \
> +                                   intermission, data_len)     \
> +)
> +
> +/*
> + * Number of bytes in a CAN frame
> + * (rounded up, including intermission)
> + */
> +#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)  \
> +       DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing, \
> +                                   true, data_len),            \
> +                    BITS_PER_BYTE)
> 
>  /*
>   * Maximum size of a Classical CAN frame
> - * (rounded up and ignoring bitstuffing)
> + * (rounded up, ignoring bitstuffing but including intermission)
>   */
> -#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF +
> CAN_MAX_DLEN)
> +#define CAN_FRAME_LEN_MAX \
> +       can_frame_bytes(false, true, false, CAN_MAX_DLEN)
> 
>  /*
>   * Maximum size of a CAN-FD frame
>   * (rounded up and ignoring bitstuffing)
Ignoring dynamic bitstuffing
>   */
> -#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF +
> CANFD_MAX_DLEN)
> +#define CANFD_FRAME_LEN_MAX \
> +       can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
> 
>  /*
>   * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
> --
> 2.39.3

I think your attribution of suggested-by for myself is mixed up for the patches 2/3 and 3/3 😊

For the entire series you can add my reviewed-by.

Thanks,
Thomas

Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent MAILHOL]

On Thu. 1 juin 2023 at19:42, <Thomas.Kopp@microchip.com> wrote:
> > Introduce a method to calculate the exact size in bits of a CAN(-FD)
> > frame with or without dynamic bitsuffing.
> >
> > These are all the possible combinations taken into account:
> >
> >   - Classical CAN or CAN-FD
> >   - Standard or Extended frame format
> >   - CAN-FD CRC17 or CRC21
> >   - Include or not intermission
> >
> > Instead of doing several individual macro definitions, declare the
> > can_frame_bits() function-like macro. To this extent, do a full
> > refactoring of the length definitions.
> >
> > In addition add the can_frame_bytes(). This function-like macro
> > replaces the existing macro:
> >
> >   - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
> >   - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
> >   - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
> >   - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
> >
> > The different maximum frame lengths (maximum data length, including
> > intermission) are as follow:
> >
> >    Frame type                           bits    bytes
> >   -------------------------------------------------------
> >    Classic CAN SFF no-bitstuffing       111     14
> >    Classic CAN EFF no-bitstuffing       131     17
> >    Classic CAN SFF bitstuffing          135     17
> >    Classic CAN EFF bitstuffing          160     20
> >    CAN-FD SFF no-bitstuffing            579     73
> >    CAN-FD EFF no-bitstuffing            598     75
> >    CAN-FD SFF bitstuffing               712     89
> >    CAN-FD EFF bitstuffing               736     92
> >
> > The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as
> > an
> > alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
> > can_frame_bytes(true, true, CANFD_MAX_DLEN).
> >
> > In addition to the above:
> >
> >  - Use ISO 11898-1:2015 definitions for the name of the CAN frame
> >    fields.
> >  - Include linux/bits.h for use of BITS_PER_BYTE.
> >  - Include linux/math.h for use of mult_frac() and
> >    DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
> >    patch, but the include was previously omitted.
> >  - Add copyright 2023 for myself.
> >
> > Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> > ---
> >  drivers/net/can/dev/length.c |  15 +-
> >  include/linux/can/length.h   | 298 +++++++++++++++++++++++++----------
> >  2 files changed, 213 insertions(+), 100 deletions(-)
> >
> > diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
> > index b48140b1102e..b7f4d76dd444 100644
> > --- a/drivers/net/can/dev/length.c
> > +++ b/drivers/net/can/dev/length.c
> > @@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct
> > sk_buff *skb)
> >         else
> >                 len = cf->len;
> >
> > -       if (can_is_canfd_skb(skb)) {
> > -               if (cf->can_id & CAN_EFF_FLAG)
> > -                       len += CANFD_FRAME_OVERHEAD_EFF;
> > -               else
> > -                       len += CANFD_FRAME_OVERHEAD_SFF;
> > -       } else {
> > -               if (cf->can_id & CAN_EFF_FLAG)
> > -                       len += CAN_FRAME_OVERHEAD_EFF;
> > -               else
> > -                       len += CAN_FRAME_OVERHEAD_SFF;
> > -       }
> > -
> > -       return len;
> > +       return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id &
> > CAN_EFF_FLAG,
> > +                              false, len);
> >  }
> >  EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
> > diff --git a/include/linux/can/length.h b/include/linux/can/length.h
> > index 521fdbce2d69..ef6e78fa95b9 100644
> > --- a/include/linux/can/length.h
> > +++ b/include/linux/can/length.h
> > @@ -1,132 +1,256 @@
> >  /* SPDX-License-Identifier: GPL-2.0 */
> >  /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
> >   * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
> > - * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> > + * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> >   */
> >
> >  #ifndef _CAN_LENGTH_H
> >  #define _CAN_LENGTH_H
> >
> > +#include <linux/bits.h>
> >  #include <linux/can.h>
> >  #include <linux/can/netlink.h>
> > +#include <linux/math.h>
> >
> >  /*
> > - * Size of a Classical CAN Standard Frame
> > + * Size of a Classical CAN Standard Frame header in bits
> >   *
> > - * Name of Field                       Bits
> > + * Name of Field                               Bits
> >   * ---------------------------------------------------------
> > - * Start-of-frame                      1
> > - * Identifier                          11
> > - * Remote transmission request (RTR)   1
> > - * Identifier extension bit (IDE)      1
> > - * Reserved bit (r0)                   1
> > - * Data length code (DLC)              4
> > - * Data field                          0...64
> > - * CRC                                 15
> > - * CRC delimiter                       1
> > - * ACK slot                            1
> > - * ACK delimiter                       1
> > - * End-of-frame (EOF)                  7
> > - * Inter frame spacing                 3
> > + * Start Of Frame (SOF)                                1
> > + * Arbitration field:
> > + *     base ID                                 11
> > + *     Remote Transmission Request (RTR)       1
> > + * Control field:
> > + *     IDentifier Extension bit (IDE)          1
> > + *     FD Format indicatior (FDF)              1
> > + *     Data Length Code (DLC)                  4
> > + *
> > + * including all fields preceding the data field, ignoring bitstuffing
> > + */
> > +#define CAN_FRAME_HEADER_SFF_BITS 19
> > +
> > +/*
> > + * Size of a Classical CAN Extended Frame header in bits
> > + *
> > + * Name of Field                               Bits
> > + * ---------------------------------------------------------
> > + * Start Of Frame (SOF)                                1
> > + * Arbitration field:
> > + *     base ID                                 11
> > + *     Substitute Remote Request (SRR)         1
> > + *     IDentifier Extension bit (IDE)          1
> > + *     ID extension                            18
> > + *     Remote Transmission Request (RTR)       1
> > + * Control field:
> > + *     FD Format indicatior (FDF)              1
> Nit: indicator, same above

ACK.

> > + *     Reserved bit (r0)                       1
> > + *     Data length code (DLC)                  4
> > + *
> > + * including all fields preceding the data field, ignoring bitstuffing
> > + */
> > +#define CAN_FRAME_HEADER_EFF_BITS 39
> > +
> > +/*
> > + * Size of a CAN-FD Standard Frame in bits
> > + *
> > + * Name of Field                               Bits
> > + * ---------------------------------------------------------
> > + * Start Of Frame (SOF)                                1
> > + * Arbitration field:
> > + *     base ID                                 11
> > + *     Remote Request Substitution (RRS)       1
> > + * Control field:
> > + *     IDentifier Extension bit (IDE)          1
> > + *     FD Format indicator (FDF)               1
> > + *     Reserved bit (res)                      1
> > + *     Bit Rate Switch (BRS)                   1
> > + *     Error Status Indicator (ESI)            1
> > + *     Data length code (DLC)                  4
> > + *
> > + * including all fields preceding the data field, ignoring bitstuffing
> > + */
> > +#define CANFD_FRAME_HEADER_SFF_BITS 22
> > +
> > +/*
> > + * Size of a CAN-FD Extended Frame in bits
> > + *
> > + * Name of Field                               Bits
> > + * ---------------------------------------------------------
> > + * Start Of Frame (SOF)                                1
> > + * Arbitration field:
> > + *     base ID                                 11
> > + *     Substitute Remote Request (SRR)         1
> > + *     IDentifier Extension bit (IDE)          1
> > + *     ID extension                            18
> > + *     Remote Request Substitution (RRS)       1
> > + * Control field:
> > + *     FD Format indicator (FDF)               1
> > + *     Reserved bit (res)                      1
> > + *     Bit Rate Switch (BRS)                   1
> > + *     Error Status Indicator (ESI)            1
> > + *     Data length code (DLC)                  4
> >   *
> > - * rounded up and ignoring bitstuffing
> > + * including all fields preceding the data field, ignoring bitstuffing
> >   */
> > -#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
> > +#define CANFD_FRAME_HEADER_EFF_BITS 41
> >
> >  /*
> > - * Size of a Classical CAN Extended Frame
> > + * Size of a CAN CRC Field in bits
> >   *
> >   * Name of Field                       Bits
> >   * ---------------------------------------------------------
> > - * Start-of-frame                      1
> > - * Identifier A                                11
> > - * Substitute remote request (SRR)     1
> > - * Identifier extension bit (IDE)      1
> > - * Identifier B                                18
> > - * Remote transmission request (RTR)   1
> > - * Reserved bits (r1, r0)              2
> > - * Data length code (DLC)              4
> > - * Data field                          0...64
> > - * CRC                                 15
> > - * CRC delimiter                       1
> > - * ACK slot                            1
> > - * ACK delimiter                       1
> > - * End-of-frame (EOF)                  7
> > - * Inter frame spacing                 3
> > + * CRC sequence (CRC15)                        15
> > + * CRC Delimiter                       1
> >   *
> > - * rounded up and ignoring bitstuffing
> > + * ignoring bitstuffing
> >   */
> > -#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
> > +#define CAN_FRAME_CRC_FIELD_BITS 16
> >
> >  /*
> > - * Size of a CAN-FD Standard Frame
> > + * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
> >   *
> >   * Name of Field                       Bits
> >   * ---------------------------------------------------------
> > - * Start-of-frame                      1
> > - * Identifier                          11
> > - * Remote Request Substitution (RRS)   1
> > - * Identifier extension bit (IDE)      1
> > - * Flexible data rate format (FDF)     1
> > - * Reserved bit (r0)                   1
> > - * Bit Rate Switch (BRS)               1
> > - * Error Status Indicator (ESI)                1
> > - * Data length code (DLC)              4
> > - * Data field                          0...512
> > - * Stuff Bit Count (SBC)               4
> > - * CRC                                 0...16: 17 20...64:21
> > - * CRC delimiter (CD)                  1
> > - * Fixed Stuff bits (FSB)              0...16: 6 20...64:7
> > - * ACK slot (AS)                       1
> > - * ACK delimiter (AD)                  1
> > - * End-of-frame (EOF)                  7
> > - * Inter frame spacing                 3
> > - *
> > - * assuming CRC21, rounded up and ignoring dynamic bitstuffing
> > - */
> > -#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
> > + * Stuff Count                         4
> > + * CRC Sequence (CRC17)                        17
> > + * CRC Delimiter                       1
> > + * Fixed stuff bits                    6
> > + */
> > +#define CANFD_FRAME_CRC17_FIELD_BITS 28
> >
> >  /*
> > - * Size of a CAN-FD Extended Frame
> > + * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
> >   *
> >   * Name of Field                       Bits
> >   * ---------------------------------------------------------
> > - * Start-of-frame                      1
> > - * Identifier A                                11
> > - * Substitute remote request (SRR)     1
> > - * Identifier extension bit (IDE)      1
> > - * Identifier B                                18
> > - * Remote Request Substitution (RRS)   1
> > - * Flexible data rate format (FDF)     1
> > - * Reserved bit (r0)                   1
> > - * Bit Rate Switch (BRS)               1
> > - * Error Status Indicator (ESI)                1
> > - * Data length code (DLC)              4
> > - * Data field                          0...512
> > - * Stuff Bit Count (SBC)               4
> > - * CRC                                 0...16: 17 20...64:21
> > - * CRC delimiter (CD)                  1
> > - * Fixed Stuff bits (FSB)              0...16: 6 20...64:7
> > - * ACK slot (AS)                       1
> > - * ACK delimiter (AD)                  1
> > - * End-of-frame (EOF)                  7
> > - * Inter frame spacing                 3
> > - *
> > - * assuming CRC21, rounded up and ignoring dynamic bitstuffing
> > - */
> > -#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
> > + * Stuff Count                         4
> > + * CRC sequence (CRC21)                        21
> > + * CRC Delimiter                       1
> > + * Fixed stuff bits                    7
> > + */
> > +#define CANFD_FRAME_CRC21_FIELD_BITS 33
> > +
> > +/*
> > + * Size of a CAN(-FD) Frame footer in bits
> > + *
> > + * Name of Field                       Bits
> > + * ---------------------------------------------------------
> > + * ACK slot                            1
> > + * ACK delimiter                       1
> > + * End Of Frame (EOF)                  7
> > + *
> > + * including all fields following the CRC field
> > + */
> > +#define CAN_FRAME_FOOTER_BITS 9
> > +
> > +/*
> > + * First part of the Inter Frame Space
> > + * (a.k.a. IMF - intermission field)
> > + */
> > +#define CAN_INTERMISSION_BITS 3
> > +
> > +/**
> > + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
> Nit: bitstuffing, same further down

ACK.

> > + * @bitstream_len: length of a destuffed bit stream
> > + *
> > + * The worst bit stuffing case is a sequence in which dominant and
> > + * recessive bits alternate every four bits:
> > + *
> > + *   Destuffed: 1 1111  0000  1111  0000  1111
> > + *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
> > + *
> > + * Nomenclature
> > + *
> > + *  - "0": dominant bit
> > + *  - "o": dominant stuff bit
> > + *  - "1": recessive bit
> > + *  - "i": recessive stuff bit
> > + *
> > + * Aside of the first bit, one stuff bit is added every four bits.
> > + *
> > + * Return: length of the stuffed bit stream in the worst case scenario.
> > + */
> > +#define can_bitstuffing_len(destuffed_len)                     \
> > +       (destuffed_len + (destuffed_len - 1) / 4)
> > +
> > +#define __can_bitstuffing_len(bitstuffing, destuffed_len)      \
> > +       (bitstuffing ? can_bitstuffing_len(destuffed_len) :     \
> > +                      destuffed_len)
> > +
> > +#define __can_cc_frame_bits(is_eff, bitstuffing,               \
> > +                           intermission, data_len)             \
> > +(                                                              \
> > +       __can_bitstuffing_len(bitstuffing,                      \
> > +               (is_eff ? CAN_FRAME_HEADER_EFF_BITS :           \
> > +                          CAN_FRAME_HEADER_SFF_BITS) +         \
> > +               data_len * BITS_PER_BYTE +                      \
> > +               CAN_FRAME_CRC_FIELD_BITS) +                     \
> > +       CAN_FRAME_FOOTER_BITS +                                 \
> > +       (intermission ? CAN_INTERMISSION_BITS : 0)              \
> > +)
> I think Footer and Intermission need to be pulled out of the parameter for __can_bitstuffing_length as these fields are never stuffed.

Look again at the opening and closing bracket of
__can_bitstuffing_len(). These are already out :)
I indented the parameters of __can_bitstuffing_length() to highlight
what is in and out.

Maybe adding some newlines would help readability? Something like that:

  #define __can_cc_frame_bits(is_eff, bitstuffing,                \
                              intermission, data_len)             \
  (                                                               \
          __can_bitstuffing_len(                                  \
                  bitstuffing,                                    \
                  (is_eff ? CAN_FRAME_HEADER_EFF_BITS :           \
                             CAN_FRAME_HEADER_SFF_BITS) +         \
                  data_len * BITS_PER_BYTE +                      \
                  CAN_FRAME_CRC_FIELD_BITS)                       \
          +                                                       \
          CAN_FRAME_FOOTER_BITS +                                 \
          (intermission ? CAN_INTERMISSION_BITS : 0)              \
  )

> > +
> > +#define __can_fd_frame_bits(is_eff, bitstuffing,               \
> > +                           intermission, data_len)             \
> > +(                                                              \
> > +       __can_bitstuffing_len(bitstuffing,                      \
> > +               (is_eff ? CANFD_FRAME_HEADER_EFF_BITS :         \
> > +                          CANFD_FRAME_HEADER_SFF_BITS) +       \
> > +               data_len * BITS_PER_BYTE) +                     \
> > +       (data_len <= 16 ?                                       \
> > +               CANFD_FRAME_CRC17_FIELD_BITS :                  \
> > +               CANFD_FRAME_CRC21_FIELD_BITS) +                 \
> > +       CAN_FRAME_FOOTER_BITS +                                 \
> > +       (intermission ? CAN_INTERMISSION_BITS : 0)              \
> > +)
> I think Footer and Intermission need to be pulled out of the parameter for __can_bitstuffing_length as these fields are never stuffed.
> The CAN_FRAME_CRC_FIELD_BITS bits need to be pulled out of the can_bitstuffing_len. That portion of the Frame is not dynamically stuffed in FD frames.

Same as above, these are already out.

> > +
> > +/**
> > + * can_frame_bits() - Calculate the number of bits in on the wire in a
> Nit: "in on the wire" -in
> > + *     CAN frame
> > + * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
> > + * @is_eff: true: Extended frame; false: Standard frame.
> > + * @bitstuffing: true: calculate the bitsuffing worst case; false:
> > + *     calculate the bitsuffing best case (no dynamic
> > + *     bitsuffing). Fixed stuff bits are always included.
> > + * @intermission: if and only if true, include the inter frame space
> > + *     assuming no bus idle (i.e. only the intermission gets added).
> > + * @data_len: length of the data field in bytes. Correspond to
> > + *     can(fd)_frame->len. Should be zero for remote frames. No
> > + *     sanitization is done on @data_len.
> > + *
> > + * Return: the numbers of bits on the wire of a CAN frame.
> > + */
> > +#define can_frame_bits(is_fd, is_eff, bitstuffing,             \
> > +                      intermission, data_len)                  \
> > +(                                                              \
> > +       is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,        \
> > +                                   intermission, data_len) :   \
> > +               __can_cc_frame_bits(is_eff, bitstuffing,        \
> > +                                   intermission, data_len)     \
> > +)
> > +
> > +/*
> > + * Number of bytes in a CAN frame
> > + * (rounded up, including intermission)
> > + */
> > +#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)  \
> > +       DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing, \
> > +                                   true, data_len),            \
> > +                    BITS_PER_BYTE)
> >
> >  /*
> >   * Maximum size of a Classical CAN frame
> > - * (rounded up and ignoring bitstuffing)
> > + * (rounded up, ignoring bitstuffing but including intermission)
> >   */
> > -#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF +
> > CAN_MAX_DLEN)
> > +#define CAN_FRAME_LEN_MAX \
> > +       can_frame_bytes(false, true, false, CAN_MAX_DLEN)
> >
> >  /*
> >   * Maximum size of a CAN-FD frame
> >   * (rounded up and ignoring bitstuffing)
> Ignoring dynamic bitstuffing
> >   */
> > -#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF +
> > CANFD_MAX_DLEN)
> > +#define CANFD_FRAME_LEN_MAX \
> > +       can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
> >
> >  /*
> >   * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
> > --
> > 2.39.3
>
> I think your attribution of suggested-by for myself is mixed up for the patches 2/3 and 3/3 😊

ACK. I will remove it from 2/3 and add it to 3/3.

> For the entire series you can add my reviewed-by.

I will do so.
Thanks for picking my typos!

RE: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

[Thomas.Kopp]

> > > Introduce a method to calculate the exact size in bits of a CAN(-FD)
> > > frame with or without dynamic bitsuffing.
> > >
> > > These are all the possible combinations taken into account:
> > >
> > >   - Classical CAN or CAN-FD
> > >   - Standard or Extended frame format
> > >   - CAN-FD CRC17 or CRC21
> > >   - Include or not intermission
> > >
> > > Instead of doing several individual macro definitions, declare the
> > > can_frame_bits() function-like macro. To this extent, do a full
> > > refactoring of the length definitions.
> > >
> > > In addition add the can_frame_bytes(). This function-like macro
> > > replaces the existing macro:
> > >
> > >   - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
> > >   - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
> > >   - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
> > >   - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)
> > >
> > > The different maximum frame lengths (maximum data length, including
> > > intermission) are as follow:
> > >
> > >    Frame type                           bits    bytes
> > >   -------------------------------------------------------
> > >    Classic CAN SFF no-bitstuffing       111     14
> > >    Classic CAN EFF no-bitstuffing       131     17
> > >    Classic CAN SFF bitstuffing          135     17
> > >    Classic CAN EFF bitstuffing          160     20
> > >    CAN-FD SFF no-bitstuffing            579     73
> > >    CAN-FD EFF no-bitstuffing            598     75
> > >    CAN-FD SFF bitstuffing               712     89
> > >    CAN-FD EFF bitstuffing               736     92
> > >
> > > The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are
> kept as
> > > an
> > > alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
> > > can_frame_bytes(true, true, CANFD_MAX_DLEN).
> > >
> > > In addition to the above:
> > >
> > >  - Use ISO 11898-1:2015 definitions for the name of the CAN frame
> > >    fields.
> > >  - Include linux/bits.h for use of BITS_PER_BYTE.
> > >  - Include linux/math.h for use of mult_frac() and
> > >    DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
> > >    patch, but the include was previously omitted.
> > >  - Add copyright 2023 for myself.
> > >
> > > Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> > > ---
> > >  drivers/net/can/dev/length.c |  15 +-
> > >  include/linux/can/length.h   | 298 +++++++++++++++++++++++++--------
> --
> > >  2 files changed, 213 insertions(+), 100 deletions(-)
> > >
> > > diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
> > > index b48140b1102e..b7f4d76dd444 100644
> > > --- a/drivers/net/can/dev/length.c
> > > +++ b/drivers/net/can/dev/length.c
> > > @@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct
> > > sk_buff *skb)
> > >         else
> > >                 len = cf->len;
> > >
> > > -       if (can_is_canfd_skb(skb)) {
> > > -               if (cf->can_id & CAN_EFF_FLAG)
> > > -                       len += CANFD_FRAME_OVERHEAD_EFF;
> > > -               else
> > > -                       len += CANFD_FRAME_OVERHEAD_SFF;
> > > -       } else {
> > > -               if (cf->can_id & CAN_EFF_FLAG)
> > > -                       len += CAN_FRAME_OVERHEAD_EFF;
> > > -               else
> > > -                       len += CAN_FRAME_OVERHEAD_SFF;
> > > -       }
> > > -
> > > -       return len;
> > > +       return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id &
> > > CAN_EFF_FLAG,
> > > +                              false, len);
> > >  }
> > >  EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
> > > diff --git a/include/linux/can/length.h b/include/linux/can/length.h
> > > index 521fdbce2d69..ef6e78fa95b9 100644
> > > --- a/include/linux/can/length.h
> > > +++ b/include/linux/can/length.h
> > > @@ -1,132 +1,256 @@
> > >  /* SPDX-License-Identifier: GPL-2.0 */
> > >  /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
> > >   * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
> > > - * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> > > + * Copyright (C) 2020, 2023 Vincent Mailhol
> <mailhol.vincent@wanadoo.fr>
> > >   */
> > >
> > >  #ifndef _CAN_LENGTH_H
> > >  #define _CAN_LENGTH_H
> > >
> > > +#include <linux/bits.h>
> > >  #include <linux/can.h>
> > >  #include <linux/can/netlink.h>
> > > +#include <linux/math.h>
> > >
> > >  /*
> > > - * Size of a Classical CAN Standard Frame
> > > + * Size of a Classical CAN Standard Frame header in bits
> > >   *
> > > - * Name of Field                       Bits
> > > + * Name of Field                               Bits
> > >   * ---------------------------------------------------------
> > > - * Start-of-frame                      1
> > > - * Identifier                          11
> > > - * Remote transmission request (RTR)   1
> > > - * Identifier extension bit (IDE)      1
> > > - * Reserved bit (r0)                   1
> > > - * Data length code (DLC)              4
> > > - * Data field                          0...64
> > > - * CRC                                 15
> > > - * CRC delimiter                       1
> > > - * ACK slot                            1
> > > - * ACK delimiter                       1
> > > - * End-of-frame (EOF)                  7
> > > - * Inter frame spacing                 3
> > > + * Start Of Frame (SOF)                                1
> > > + * Arbitration field:
> > > + *     base ID                                 11
> > > + *     Remote Transmission Request (RTR)       1
> > > + * Control field:
> > > + *     IDentifier Extension bit (IDE)          1
> > > + *     FD Format indicatior (FDF)              1
> > > + *     Data Length Code (DLC)                  4
> > > + *
> > > + * including all fields preceding the data field, ignoring bitstuffing
> > > + */
> > > +#define CAN_FRAME_HEADER_SFF_BITS 19
> > > +
> > > +/*
> > > + * Size of a Classical CAN Extended Frame header in bits
> > > + *
> > > + * Name of Field                               Bits
> > > + * ---------------------------------------------------------
> > > + * Start Of Frame (SOF)                                1
> > > + * Arbitration field:
> > > + *     base ID                                 11
> > > + *     Substitute Remote Request (SRR)         1
> > > + *     IDentifier Extension bit (IDE)          1
> > > + *     ID extension                            18
> > > + *     Remote Transmission Request (RTR)       1
> > > + * Control field:
> > > + *     FD Format indicatior (FDF)              1
> > Nit: indicator, same above
> 
> ACK.
> 
> > > + *     Reserved bit (r0)                       1
> > > + *     Data length code (DLC)                  4
> > > + *
> > > + * including all fields preceding the data field, ignoring bitstuffing
> > > + */
> > > +#define CAN_FRAME_HEADER_EFF_BITS 39
> > > +
> > > +/*
> > > + * Size of a CAN-FD Standard Frame in bits
> > > + *
> > > + * Name of Field                               Bits
> > > + * ---------------------------------------------------------
> > > + * Start Of Frame (SOF)                                1
> > > + * Arbitration field:
> > > + *     base ID                                 11
> > > + *     Remote Request Substitution (RRS)       1
> > > + * Control field:
> > > + *     IDentifier Extension bit (IDE)          1
> > > + *     FD Format indicator (FDF)               1
> > > + *     Reserved bit (res)                      1
> > > + *     Bit Rate Switch (BRS)                   1
> > > + *     Error Status Indicator (ESI)            1
> > > + *     Data length code (DLC)                  4
> > > + *
> > > + * including all fields preceding the data field, ignoring bitstuffing
> > > + */
> > > +#define CANFD_FRAME_HEADER_SFF_BITS 22
> > > +
> > > +/*
> > > + * Size of a CAN-FD Extended Frame in bits
> > > + *
> > > + * Name of Field                               Bits
> > > + * ---------------------------------------------------------
> > > + * Start Of Frame (SOF)                                1
> > > + * Arbitration field:
> > > + *     base ID                                 11
> > > + *     Substitute Remote Request (SRR)         1
> > > + *     IDentifier Extension bit (IDE)          1
> > > + *     ID extension                            18
> > > + *     Remote Request Substitution (RRS)       1
> > > + * Control field:
> > > + *     FD Format indicator (FDF)               1
> > > + *     Reserved bit (res)                      1
> > > + *     Bit Rate Switch (BRS)                   1
> > > + *     Error Status Indicator (ESI)            1
> > > + *     Data length code (DLC)                  4
> > >   *
> > > - * rounded up and ignoring bitstuffing
> > > + * including all fields preceding the data field, ignoring bitstuffing
> > >   */
> > > -#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
> > > +#define CANFD_FRAME_HEADER_EFF_BITS 41
> > >
> > >  /*
> > > - * Size of a Classical CAN Extended Frame
> > > + * Size of a CAN CRC Field in bits
> > >   *
> > >   * Name of Field                       Bits
> > >   * ---------------------------------------------------------
> > > - * Start-of-frame                      1
> > > - * Identifier A                                11
> > > - * Substitute remote request (SRR)     1
> > > - * Identifier extension bit (IDE)      1
> > > - * Identifier B                                18
> > > - * Remote transmission request (RTR)   1
> > > - * Reserved bits (r1, r0)              2
> > > - * Data length code (DLC)              4
> > > - * Data field                          0...64
> > > - * CRC                                 15
> > > - * CRC delimiter                       1
> > > - * ACK slot                            1
> > > - * ACK delimiter                       1
> > > - * End-of-frame (EOF)                  7
> > > - * Inter frame spacing                 3
> > > + * CRC sequence (CRC15)                        15
> > > + * CRC Delimiter                       1
> > >   *
> > > - * rounded up and ignoring bitstuffing
> > > + * ignoring bitstuffing
> > >   */
> > > -#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
> > > +#define CAN_FRAME_CRC_FIELD_BITS 16
> > >
> > >  /*
> > > - * Size of a CAN-FD Standard Frame
> > > + * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
> > >   *
> > >   * Name of Field                       Bits
> > >   * ---------------------------------------------------------
> > > - * Start-of-frame                      1
> > > - * Identifier                          11
> > > - * Remote Request Substitution (RRS)   1
> > > - * Identifier extension bit (IDE)      1
> > > - * Flexible data rate format (FDF)     1
> > > - * Reserved bit (r0)                   1
> > > - * Bit Rate Switch (BRS)               1
> > > - * Error Status Indicator (ESI)                1
> > > - * Data length code (DLC)              4
> > > - * Data field                          0...512
> > > - * Stuff Bit Count (SBC)               4
> > > - * CRC                                 0...16: 17 20...64:21
> > > - * CRC delimiter (CD)                  1
> > > - * Fixed Stuff bits (FSB)              0...16: 6 20...64:7
> > > - * ACK slot (AS)                       1
> > > - * ACK delimiter (AD)                  1
> > > - * End-of-frame (EOF)                  7
> > > - * Inter frame spacing                 3
> > > - *
> > > - * assuming CRC21, rounded up and ignoring dynamic bitstuffing
> > > - */
> > > -#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
> > > + * Stuff Count                         4
> > > + * CRC Sequence (CRC17)                        17
> > > + * CRC Delimiter                       1
> > > + * Fixed stuff bits                    6
> > > + */
> > > +#define CANFD_FRAME_CRC17_FIELD_BITS 28
> > >
> > >  /*
> > > - * Size of a CAN-FD Extended Frame
> > > + * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
> > >   *
> > >   * Name of Field                       Bits
> > >   * ---------------------------------------------------------
> > > - * Start-of-frame                      1
> > > - * Identifier A                                11
> > > - * Substitute remote request (SRR)     1
> > > - * Identifier extension bit (IDE)      1
> > > - * Identifier B                                18
> > > - * Remote Request Substitution (RRS)   1
> > > - * Flexible data rate format (FDF)     1
> > > - * Reserved bit (r0)                   1
> > > - * Bit Rate Switch (BRS)               1
> > > - * Error Status Indicator (ESI)                1
> > > - * Data length code (DLC)              4
> > > - * Data field                          0...512
> > > - * Stuff Bit Count (SBC)               4
> > > - * CRC                                 0...16: 17 20...64:21
> > > - * CRC delimiter (CD)                  1
> > > - * Fixed Stuff bits (FSB)              0...16: 6 20...64:7
> > > - * ACK slot (AS)                       1
> > > - * ACK delimiter (AD)                  1
> > > - * End-of-frame (EOF)                  7
> > > - * Inter frame spacing                 3
> > > - *
> > > - * assuming CRC21, rounded up and ignoring dynamic bitstuffing
> > > - */
> > > -#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
> > > + * Stuff Count                         4
> > > + * CRC sequence (CRC21)                        21
> > > + * CRC Delimiter                       1
> > > + * Fixed stuff bits                    7
> > > + */
> > > +#define CANFD_FRAME_CRC21_FIELD_BITS 33
> > > +
> > > +/*
> > > + * Size of a CAN(-FD) Frame footer in bits
> > > + *
> > > + * Name of Field                       Bits
> > > + * ---------------------------------------------------------
> > > + * ACK slot                            1
> > > + * ACK delimiter                       1
> > > + * End Of Frame (EOF)                  7
> > > + *
> > > + * including all fields following the CRC field
> > > + */
> > > +#define CAN_FRAME_FOOTER_BITS 9
> > > +
> > > +/*
> > > + * First part of the Inter Frame Space
> > > + * (a.k.a. IMF - intermission field)
> > > + */
> > > +#define CAN_INTERMISSION_BITS 3
> > > +
> > > +/**
> > > + * can_bitstuffing_len() - Calculate the maximum length with bitsuffing
> > Nit: bitstuffing, same further down
> 
> ACK.
> 
> > > + * @bitstream_len: length of a destuffed bit stream
> > > + *
> > > + * The worst bit stuffing case is a sequence in which dominant and
> > > + * recessive bits alternate every four bits:
> > > + *
> > > + *   Destuffed: 1 1111  0000  1111  0000  1111
> > > + *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
> > > + *
> > > + * Nomenclature
> > > + *
> > > + *  - "0": dominant bit
> > > + *  - "o": dominant stuff bit
> > > + *  - "1": recessive bit
> > > + *  - "i": recessive stuff bit
> > > + *
> > > + * Aside of the first bit, one stuff bit is added every four bits.
> > > + *
> > > + * Return: length of the stuffed bit stream in the worst case scenario.
> > > + */
> > > +#define can_bitstuffing_len(destuffed_len)                     \
> > > +       (destuffed_len + (destuffed_len - 1) / 4)
> > > +
> > > +#define __can_bitstuffing_len(bitstuffing, destuffed_len)      \
> > > +       (bitstuffing ? can_bitstuffing_len(destuffed_len) :     \
> > > +                      destuffed_len)
> > > +
> > > +#define __can_cc_frame_bits(is_eff, bitstuffing,               \
> > > +                           intermission, data_len)             \
> > > +(                                                              \
> > > +       __can_bitstuffing_len(bitstuffing,                      \
> > > +               (is_eff ? CAN_FRAME_HEADER_EFF_BITS :           \
> > > +                          CAN_FRAME_HEADER_SFF_BITS) +         \
> > > +               data_len * BITS_PER_BYTE +                      \
> > > +               CAN_FRAME_CRC_FIELD_BITS) +                     \
> > > +       CAN_FRAME_FOOTER_BITS +                                 \
> > > +       (intermission ? CAN_INTERMISSION_BITS : 0)              \
> > > +)
> > I think Footer and Intermission need to be pulled out of the parameter for
> __can_bitstuffing_length as these fields are never stuffed.
> 
> Look again at the opening and closing bracket of
> __can_bitstuffing_len(). These are already out :)
> I indented the parameters of __can_bitstuffing_length() to highlight
> what is in and out.
> 
> Maybe adding some newlines would help readability? Something like that:
> 
>   #define __can_cc_frame_bits(is_eff, bitstuffing,                \
>                               intermission, data_len)             \
>   (                                                               \
>           __can_bitstuffing_len(                                  \
>                   bitstuffing,                                    \
>                   (is_eff ? CAN_FRAME_HEADER_EFF_BITS :           \
>                              CAN_FRAME_HEADER_SFF_BITS) +         \
>                   data_len * BITS_PER_BYTE +                      \
>                   CAN_FRAME_CRC_FIELD_BITS)                       \
>           +                                                       \
>           CAN_FRAME_FOOTER_BITS +                                 \
>           (intermission ? CAN_INTERMISSION_BITS : 0)              \
>   )
> 
> > > +
> > > +#define __can_fd_frame_bits(is_eff, bitstuffing,               \
> > > +                           intermission, data_len)             \
> > > +(                                                              \
> > > +       __can_bitstuffing_len(bitstuffing,                      \
> > > +               (is_eff ? CANFD_FRAME_HEADER_EFF_BITS :         \
> > > +                          CANFD_FRAME_HEADER_SFF_BITS) +       \
> > > +               data_len * BITS_PER_BYTE) +                     \
> > > +       (data_len <= 16 ?                                       \
> > > +               CANFD_FRAME_CRC17_FIELD_BITS :                  \
> > > +               CANFD_FRAME_CRC21_FIELD_BITS) +                 \
> > > +       CAN_FRAME_FOOTER_BITS +                                 \
> > > +       (intermission ? CAN_INTERMISSION_BITS : 0)              \
> > > +)
> > I think Footer and Intermission need to be pulled out of the parameter for
> __can_bitstuffing_length as these fields are never stuffed.
> > The CAN_FRAME_CRC_FIELD_BITS bits need to be pulled out of the
> can_bitstuffing_len. That portion of the Frame is not dynamically stuffed in FD
> frames.
> 
> Same as above, these are already out.
Whoops - my bad, re-reading these portions both old and new look ok to me. No need for extra newlines from my point of view, just better attention at the reader side to the indentation which is already there - that greatly helps 😉

> 
> > > +
> > > +/**
> > > + * can_frame_bits() - Calculate the number of bits in on the wire in a
> > Nit: "in on the wire" -in
> > > + *     CAN frame
> > > + * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
> > > + * @is_eff: true: Extended frame; false: Standard frame.
> > > + * @bitstuffing: true: calculate the bitsuffing worst case; false:
> > > + *     calculate the bitsuffing best case (no dynamic
> > > + *     bitsuffing). Fixed stuff bits are always included.
> > > + * @intermission: if and only if true, include the inter frame space
> > > + *     assuming no bus idle (i.e. only the intermission gets added).
> > > + * @data_len: length of the data field in bytes. Correspond to
> > > + *     can(fd)_frame->len. Should be zero for remote frames. No
> > > + *     sanitization is done on @data_len.
> > > + *
> > > + * Return: the numbers of bits on the wire of a CAN frame.
> > > + */
> > > +#define can_frame_bits(is_fd, is_eff, bitstuffing,             \
> > > +                      intermission, data_len)                  \
> > > +(                                                              \
> > > +       is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,        \
> > > +                                   intermission, data_len) :   \
> > > +               __can_cc_frame_bits(is_eff, bitstuffing,        \
> > > +                                   intermission, data_len)     \
> > > +)
> > > +
> > > +/*
> > > + * Number of bytes in a CAN frame
> > > + * (rounded up, including intermission)
> > > + */
> > > +#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)  \
> > > +       DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing, \
> > > +                                   true, data_len),            \
> > > +                    BITS_PER_BYTE)
> > >
> > >  /*
> > >   * Maximum size of a Classical CAN frame
> > > - * (rounded up and ignoring bitstuffing)
> > > + * (rounded up, ignoring bitstuffing but including intermission)
> > >   */
> > > -#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF +
> > > CAN_MAX_DLEN)
> > > +#define CAN_FRAME_LEN_MAX \
> > > +       can_frame_bytes(false, true, false, CAN_MAX_DLEN)
> > >
> > >  /*
> > >   * Maximum size of a CAN-FD frame
> > >   * (rounded up and ignoring bitstuffing)
> > Ignoring dynamic bitstuffing
> > >   */
> > > -#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF +
> > > CANFD_MAX_DLEN)
> > > +#define CANFD_FRAME_LEN_MAX \
> > > +       can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
> > >
> > >  /*
> > >   * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
> > > --
> > > 2.39.3
> >
> > I think your attribution of suggested-by for myself is mixed up for the
> patches 2/3 and 3/3 😊
> 
> ACK. I will remove it from 2/3 and add it to 3/3.
> 
> > For the entire series you can add my reviewed-by.
> 
> I will do so.
> Thanks for picking my typos!

Best Regards,
Thomas

[PATCH v4 0/3] can: length: fix definitions and add bit length calculation

[Vincent Mailhol]

When created in [1], frames length definitions were added to implement
byte queue limits (bql). Because bql expects lengths in bytes, bit
length definitions were not considered back then.
    
Recently, a need to refer to the exact frame length in bits, with CAN
bit stuffing, appeared in [2].

This series introduces can_frame_bits(): a function-like macro that
can calculate the exact size of a CAN(-FD) frame in bits with or
without bitsuffing.

[1] commit 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce
    function to get data length of frame in data link layer")
Link: https://git.kernel.org/torvalds/c/85d99c3e2a13

[2] RE: [PATCH] can: mcp251xfd: Increase poll timeout
Link: https://lore.kernel.org/linux-can/BL3PR11MB64846C83ACD04E9330B0FE66FB729@BL3PR11MB6484.namprd11.prod.outlook.com/


* Changelog *

v3 -> v4:

  * No functional changes.

  * as reported by Simon Horman, fix typo in the documentation of
    can_bitstuffing_len(): "bitstream_len" -> "destuffed_len".

  * as reported by Thomas Kopp, fix several other typos:
      - "indicatior" -> "indicator"
      - "in on the wire" -> "on the wire"
      - "bitsuffing" -> "bitstuffing".

  * in CAN_FRAME_LEN_MAX comment: specify that only the dynamic
    bitstuffing gets ignored but that the intermission is included.

  * move the Suggested-by: Thomas Kopp tag from patch 2 to patch 3.

  * add Reviewed-by: Thomas Kopp tag on the full series.

  * add an additional line of comment for the @intermission argument
    of can_frame_bits().

Link: https://lore.kernel.org/linux-can/20230530144637.4746-1-mailhol.vincent@wanadoo.fr/

v2 -> v3:

  * turn can_frame_bits() and can_frame_bytes() into function-like
    macros. The fact that inline functions can not be used to
    initialize constant struct fields was bothering me. I did my best
    to make the macro look as less ugly as possible.

  * as reported by Simon Horman, add missing document for the is_fd
    argument of can_frame_bits().

Link: https://lore.kernel.org/linux-can/20230523065218.51227-1-mailhol.vincent@wanadoo.fr/

v1 -> v2:

  * as suggested by Thomas Kopp, add a new patch to the series to fix
    the stuff bit count and the fixed stuff bits definitions

  * and another patch to fix documentation of the Remote Request
    Substitution (RRS).

  * refactor the length definition. Instead of using individual macro,
    rely on an inline function. One reason is to minimize the number
    of definitions. Another reason is that because the dynamic bit
    stuff is calculated differently for CAN and CAN-FD, it is just not
    possible to multiply the existing CANFD_FRAME_OVERHEAD_SFF/EFF by
    the overhead ratio to get the bitsuffing: for CAN-FD, the CRC
    field is already stuffed by the fixed stuff bits and is out of
    scope of the dynamic bitstuffing.

Link: https://lore.kernel.org/linux-can/20230507155506.3179711-1-mailhol.vincent@wanadoo.fr/

Vincent Mailhol (3):
  can: length: fix bitstuffing count
  can: length: fix description of the RRS field
  can: length: refactor frame lengths definition to add size in bits

 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 300 +++++++++++++++++++++++++----------
 2 files changed, 217 insertions(+), 98 deletions(-)

-- 
2.39.3

[PATCH v4 1/3] can: length: fix bitstuffing count

[Vincent Mailhol]

The Stuff Bit Count is always coded on 4 bits (ref [1]). Update the
Stuff Bit Count size accordingly.

In addition, the CRC fields of CAN FD Frames contain stuff bits at
fixed positions called fixed stuff bits [2]. The CRC field starts with
a fixed stuff bit and then has another fixed stuff bit after each
fourth bit [2], which allow us to derive this formula:

  FSB count = 1 + round_down(len(CRC field)/4)

The length of the CRC field is [1]:

  len(CRC field) = len(Stuff Bit Count) + len(CRC)
                 = 4 + len(CRC)

with len(CRC) either 17 or 21 bits depending of the payload length.

In conclusion, for CRC17:

  FSB count = 1 + round_down((4 + 17)/4)
            = 6

and for CRC 21:

  FSB count = 1 + round_down((4 + 21)/4)
            = 7

Add a Fixed Stuff bits (FSB) field with above values and update
CANFD_FRAME_OVERHEAD_SFF and CANFD_FRAME_OVERHEAD_EFF accordingly.

[1] ISO 11898-1:2015 section 10.4.2.6 "CRC field":

  The CRC field shall contain the CRC sequence followed by a recessive
  CRC delimiter. For FD Frames, the CRC field shall also contain the
  stuff count.

  Stuff count

  If FD Frames, the stuff count shall be at the beginning of the CRC
  field. It shall consist of the stuff bit count modulo 8 in a 3-bit
  gray code followed by a parity bit [...]

[2] ISO 11898-1:2015 paragraph 10.5 "Frame coding":

  In the CRC field of FD Frames, the stuff bits shall be inserted at
  fixed positions; they are called fixed stuff bits. There shall be a
  fixed stuff bit before the first bit of the stuff count, even if the
  last bits of the preceding field are a sequence of five consecutive
  bits of identical value, there shall be only the fixed stuff bit,
  there shall not be two consecutive stuff bits. A further fixed stuff
  bit shall be inserted after each fourth bit of the CRC field [...]

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
---
 include/linux/can/length.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 69336549d24f..b8c12c83bc51 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -72,17 +72,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
+#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
 
 /*
  * Size of a CAN-FD Extended Frame
@@ -101,17 +102,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
+#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
 
 /*
  * Maximum size of a Classical CAN frame
-- 
2.39.3

[PATCH v4 2/3] can: length: fix description of the RRS field

[Vincent Mailhol]

The CAN-FD frames only have one reserved bit. The bit corresponding to
Classical CAN frame's RTR bit is called the "Remote Request
Substitution (RRS)" [1].

N.B. The RRS is not to be confused with the Substitute remote request
(SRR).

Fix the description in the CANFD_FRAME_OVERHEAD_SFF/EFF.

The total remains unchanged, so this is just a documentation fix.

In addition to the above add myself as copyright owner for 2020 (as
coauthor of the initial version, c.f. Fixes tag).

[1] ISO 11898-1:2015 paragraph 10.4.2.3 "Arbitration field":

  RSS bit [only in FD Frames]

    The RRS bit shall be transmitted in FD Frames at the position of
    the RTR bit in Classical Frames. The RRS bit shall be transmitted
    dominant, but receivers shall accept recessive and dominant RRS
    bits.

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
---
 include/linux/can/length.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index b8c12c83bc51..521fdbce2d69 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
+ * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
@@ -64,7 +65,7 @@
  * ---------------------------------------------------------
  * Start-of-frame			1
  * Identifier				11
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Identifier extension bit (IDE)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
@@ -95,7 +96,7 @@
  * Substitute remote request (SRR)	1
  * Identifier extension bit (IDE)	1
  * Identifier B				18
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
  * Bit Rate Switch (BRS)		1
-- 
2.39.3

[PATCH v4 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent Mailhol]

Introduce a method to calculate the exact size in bits of a CAN(-FD)
frame with or without dynamic bitstuffing.

These are all the possible combinations taken into account:

  - Classical CAN or CAN-FD
  - Standard or Extended frame format
  - CAN-FD CRC17 or CRC21
  - Include or not intermission

Instead of doing several individual macro definitions, declare the
can_frame_bits() function-like macro. To this extent, do a full
refactoring of the length definitions.

In addition add the can_frame_bytes(). This function-like macro
replaces the existing macro:

  - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
  - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
  - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
  - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)

Function-like macros were chosen over inline functions because they
can be used to initialize in const struct fields.

The different maximum frame lengths (maximum data length, including
intermission) are as follow:

   Frame type				bits	bytes
  -------------------------------------------------------
   Classic CAN SFF no bitstuffing	111	14
   Classic CAN EFF no bitstuffing	131	17
   Classic CAN SFF bitstuffing		135	17
   Classic CAN EFF bitstuffing		160	20
   CAN-FD SFF no bitstuffing		579	73
   CAN-FD EFF no bitstuffing		598	75
   CAN-FD SFF bitstuffing		712	89
   CAN-FD EFF bitstuffing		736	92

The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
can_frame_bytes(true, true, CANFD_MAX_DLEN).

In addition to the above:

 - Use ISO 11898-1:2015 definitions for the names of the CAN frame
   fields.
 - Include linux/bits.h for use of BITS_PER_BYTE.
 - Include linux/math.h for use of mult_frac() and
   DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
   patch, but the include was previously omitted.
 - Add copyright 2023 for myself.

Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
---
 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 303 +++++++++++++++++++++++++----------
 2 files changed, 217 insertions(+), 101 deletions(-)

diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
index b48140b1102e..b7f4d76dd444 100644
--- a/drivers/net/can/dev/length.c
+++ b/drivers/net/can/dev/length.c
@@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
 	else
 		len = cf->len;
 
-	if (can_is_canfd_skb(skb)) {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CANFD_FRAME_OVERHEAD_EFF;
-		else
-			len += CANFD_FRAME_OVERHEAD_SFF;
-	} else {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CAN_FRAME_OVERHEAD_EFF;
-		else
-			len += CAN_FRAME_OVERHEAD_SFF;
-	}
-
-	return len;
+	return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,
+			       false, len);
 }
 EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 521fdbce2d69..637b9322db82 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,132 +1,259 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
- * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
+ * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
 #define _CAN_LENGTH_H
 
+#include <linux/bits.h>
 #include <linux/can.h>
 #include <linux/can/netlink.h>
+#include <linux/math.h>
 
 /*
- * Size of a Classical CAN Standard Frame
+ * Size of a Classical CAN Standard Frame header in bits
  *
- * Name of Field			Bits
+ * Name of Field				Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote transmission request (RTR)	1
- * Identifier extension bit (IDE)	1
- * Reserved bit (r0)			1
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicator (FDF)		1
+ *	Data Length Code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CAN_FRAME_HEADER_SFF_BITS 19
+
+/*
+ * Size of a Classical CAN Extended Frame header in bits
  *
- * rounded up and ignoring bitstuffing
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (r0)			1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
  */
-#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+#define CAN_FRAME_HEADER_EFF_BITS 39
 
 /*
- * Size of a Classical CAN Extended Frame
+ * Size of a CAN-FD Standard Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_SFF_BITS 22
+
+/*
+ * Size of a CAN-FD Extended Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_EFF_BITS 41
+
+/*
+ * Size of a CAN CRC Field in bits
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote transmission request (RTR)	1
- * Reserved bits (r1, r0)		2
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * CRC sequence (CRC15)			15
+ * CRC Delimiter			1
+ *
+ * ignoring bitstuffing
+ */
+#define CAN_FRAME_CRC_FIELD_BITS 16
+
+/*
+ * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
  *
- * rounded up and ignoring bitstuffing
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Stuff Count				4
+ * CRC Sequence (CRC17)			17
+ * CRC Delimiter			1
+ * Fixed stuff bits			6
  */
-#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+#define CANFD_FRAME_CRC17_FIELD_BITS 28
 
 /*
- * Size of a CAN-FD Standard Frame
+ * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote Request Substitution (RRS)	1
- * Identifier extension bit (IDE)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
- */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
+ * Stuff Count				4
+ * CRC sequence (CRC21)			21
+ * CRC Delimiter			1
+ * Fixed stuff bits			7
+ */
+#define CANFD_FRAME_CRC21_FIELD_BITS 33
 
 /*
- * Size of a CAN-FD Extended Frame
+ * Size of a CAN(-FD) Frame footer in bits
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote Request Substitution (RRS)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
- */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
+ * ACK slot				1
+ * ACK delimiter			1
+ * End Of Frame (EOF)			7
+ *
+ * including all fields following the CRC field
+ */
+#define CAN_FRAME_FOOTER_BITS 9
+
+/*
+ * First part of the Inter Frame Space
+ * (a.k.a. IMF - intermission field)
+ */
+#define CAN_INTERMISSION_BITS 3
+
+/**
+ * can_bitstuffing_len() - Calculate the maximum length with bitstuffing
+ * @destuffed_len: length of a destuffed bit stream
+ *
+ * The worst bit stuffing case is a sequence in which dominant and
+ * recessive bits alternate every four bits:
+ *
+ *   Destuffed: 1 1111  0000  1111  0000  1111
+ *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
+ *
+ * Nomenclature
+ *
+ *  - "0": dominant bit
+ *  - "o": dominant stuff bit
+ *  - "1": recessive bit
+ *  - "i": recessive stuff bit
+ *
+ * Aside from the first bit, one stuff bit is added every four bits.
+ *
+ * Return: length of the stuffed bit stream in the worst case scenario.
+ */
+#define can_bitstuffing_len(destuffed_len)			\
+	(destuffed_len + (destuffed_len - 1) / 4)
+
+#define __can_bitstuffing_len(bitstuffing, destuffed_len)	\
+	(bitstuffing ? can_bitstuffing_len(destuffed_len) :	\
+		       destuffed_len)
+
+#define __can_cc_frame_bits(is_eff, bitstuffing,		\
+			    intermission, data_len)		\
+(								\
+	__can_bitstuffing_len(bitstuffing,			\
+		(is_eff ? CAN_FRAME_HEADER_EFF_BITS :		\
+			  CAN_FRAME_HEADER_SFF_BITS) +		\
+		data_len * BITS_PER_BYTE +			\
+		CAN_FRAME_CRC_FIELD_BITS) +			\
+	CAN_FRAME_FOOTER_BITS +					\
+	(intermission ? CAN_INTERMISSION_BITS : 0)		\
+)
+
+#define __can_fd_frame_bits(is_eff, bitstuffing,		\
+			    intermission, data_len)		\
+(								\
+	__can_bitstuffing_len(bitstuffing,			\
+		(is_eff ? CANFD_FRAME_HEADER_EFF_BITS :		\
+			  CANFD_FRAME_HEADER_SFF_BITS) +	\
+		data_len * BITS_PER_BYTE) +			\
+	(data_len <= 16 ?					\
+		CANFD_FRAME_CRC17_FIELD_BITS :			\
+		CANFD_FRAME_CRC21_FIELD_BITS) +			\
+	CAN_FRAME_FOOTER_BITS +					\
+	(intermission ? CAN_INTERMISSION_BITS : 0)		\
+)
+
+/**
+ * can_frame_bits() - Calculate the number of bits on the wire in a
+ *	CAN frame
+ * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
+ * @is_eff: true: Extended frame; false: Standard frame.
+ * @bitstuffing: true: calculate the bitstuffing worst case; false:
+ *	calculate the bitstuffing best case (no dynamic
+ *	bitstuffing). CAN-FD's fixed stuff bits are always included.
+ * @intermission: if and only if true, include the inter frame space
+ *	assuming no bus idle (i.e. only the intermission). Strictly
+ *	speaking, the inter frame space is not part of the
+ *	frame. However, it is needed when calculating the delay
+ *	between the Start Of Frame of two consecutive frames.
+ * @data_len: length of the data field in bytes. Correspond to
+ *	can(fd)_frame->len. Should be zero for remote frames. No
+ *	sanitization is done on @data_len.
+ *
+ * Return: the numbers of bits on the wire of a CAN frame.
+ */
+#define can_frame_bits(is_fd, is_eff, bitstuffing,		\
+		       intermission, data_len)			\
+(								\
+	is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,	\
+				    intermission, data_len) :	\
+		__can_cc_frame_bits(is_eff, bitstuffing,	\
+				    intermission, data_len)	\
+)
+
+/*
+ * Number of bytes in a CAN frame
+ * (rounded up, including intermission)
+ */
+#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)	\
+	DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing,	\
+				    true, data_len),		\
+		     BITS_PER_BYTE)
 
 /*
  * Maximum size of a Classical CAN frame
- * (rounded up and ignoring bitstuffing)
+ * (rounded up, ignoring bitstuffing but including intermission)
  */
-#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)
+#define CAN_FRAME_LEN_MAX \
+	can_frame_bytes(false, true, false, CAN_MAX_DLEN)
 
 /*
  * Maximum size of a CAN-FD frame
- * (rounded up and ignoring bitstuffing)
+ * (rounded up, ignoring dynamic bitstuffing but including intermission)
  */
-#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)
+#define CANFD_FRAME_LEN_MAX \
+	can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
 
 /*
  * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
-- 
2.39.3

[PATCH v5 0/3] can: length: fix definitions and add bit length calculation

[Vincent Mailhol]

When created in [1], frames length definitions were added to implement
byte queue limits (bql). Because bql expects lengths in bytes, bit
length definitions were not considered back then.
    
Recently, a need to refer to the exact frame length in bits, with CAN
bit stuffing, appeared in [2].

This series introduces can_frame_bits(): a function-like macro that
can calculate the exact size of a CAN(-FD) frame in bits with or
without bitsuffing.

[1] commit 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce
    function to get data length of frame in data link layer")
Link: https://git.kernel.org/torvalds/c/85d99c3e2a13

[2] RE: [PATCH] can: mcp251xfd: Increase poll timeout
Link: https://lore.kernel.org/linux-can/BL3PR11MB64846C83ACD04E9330B0FE66FB729@BL3PR11MB6484.namprd11.prod.outlook.com/


* Changelog *

v4 -> v5:

  * In __can_cc_frame_bits() and __can_fd_frame_bits(), enclose
    data_len in brackets to prevent operator precedence issues.

  * Add a note in can_frame_bits() documentation to explain that
    data_len shall have no side effects.

  * While at it, make CAN(FD)_FRAME_LEN_MAX definition fit on a single
    line.

  * A few typo/grammar small fixes in the commit descriptions.

Link: https://lore.kernel.org/linux-can/20230601165625.100040-1-mailhol.vincent@wanadoo.fr/

v3 -> v4:

  * No functional changes.

  * as reported by Simon Horman, fix typo in the documentation of
    can_bitstuffing_len(): "bitstream_len" -> "destuffed_len".

  * as reported by Thomas Kopp, fix several other typos:
      - "indicatior" -> "indicator"
      - "in on the wire" -> "on the wire"
      - "bitsuffing" -> "bitstuffing".

  * in CAN_FRAME_LEN_MAX comment: specify that only the dynamic
    bitstuffing gets ignored but that the intermission is included.

  * move the Suggested-by: Thomas Kopp tag from patch 2 to patch 3.

  * add Reviewed-by: Thomas Kopp tag on the full series.

  * add an additional line of comment for the @intermission argument
    of can_frame_bits().

Link: https://lore.kernel.org/linux-can/20230530144637.4746-1-mailhol.vincent@wanadoo.fr/

v2 -> v3:

  * turn can_frame_bits() and can_frame_bytes() into function-like
    macros. The fact that inline functions can not be used to
    initialize constant struct fields was bothering me. I did my best
    to make the macro look as less ugly as possible.

  * as reported by Simon Horman, add missing document for the is_fd
    argument of can_frame_bits().

Link: https://lore.kernel.org/linux-can/20230523065218.51227-1-mailhol.vincent@wanadoo.fr/

v1 -> v2:

  * as suggested by Thomas Kopp, add a new patch to the series to fix
    the stuff bit count and the fixed stuff bits definitions

  * and another patch to fix documentation of the Remote Request
    Substitution (RRS).

  * refactor the length definition. Instead of using individual macro,
    rely on an inline function. One reason is to minimize the number
    of definitions. Another reason is that because the dynamic bit
    stuff is calculated differently for CAN and CAN-FD, it is just not
    possible to multiply the existing CANFD_FRAME_OVERHEAD_SFF/EFF by
    the overhead ratio to get the bitsuffing: for CAN-FD, the CRC
    field is already stuffed by the fixed stuff bits and is out of
    scope of the dynamic bitstuffing.

Link: https://lore.kernel.org/linux-can/20230507155506.3179711-1-mailhol.vincent@wanadoo.fr/

Vincent Mailhol (3):
  can: length: fix bitstuffing count
  can: length: fix description of the RRS field
  can: length: refactor frame lengths definition to add size in bits

 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 299 +++++++++++++++++++++++++----------
 2 files changed, 216 insertions(+), 98 deletions(-)

-- 
2.39.3

[PATCH v5 1/3] can: length: fix bitstuffing count

[Vincent Mailhol]

The Stuff Bit Count is always coded on 4 bits [1]. Update the Stuff
Bit Count size accordingly.

In addition, the CRC fields of CAN FD Frames contain stuff bits at
fixed positions called fixed stuff bits [2]. The CRC field starts with
a fixed stuff bit and then has another fixed stuff bit after each
fourth bit [2], which allows us to derive this formula:

  FSB count = 1 + round_down(len(CRC field)/4)

The length of the CRC field is [1]:

  len(CRC field) = len(Stuff Bit Count) + len(CRC)
                 = 4 + len(CRC)

with len(CRC) either 17 or 21 bits depending of the payload length.

In conclusion, for CRC17:

  FSB count = 1 + round_down((4 + 17)/4)
            = 6

and for CRC 21:

  FSB count = 1 + round_down((4 + 21)/4)
            = 7

Add a Fixed Stuff bits (FSB) field with above values and update
CANFD_FRAME_OVERHEAD_SFF and CANFD_FRAME_OVERHEAD_EFF accordingly.

[1] ISO 11898-1:2015 section 10.4.2.6 "CRC field":

  The CRC field shall contain the CRC sequence followed by a recessive
  CRC delimiter. For FD Frames, the CRC field shall also contain the
  stuff count.

  Stuff count

  If FD Frames, the stuff count shall be at the beginning of the CRC
  field. It shall consist of the stuff bit count modulo 8 in a 3-bit
  gray code followed by a parity bit [...]

[2] ISO 11898-1:2015 paragraph 10.5 "Frame coding":

  In the CRC field of FD Frames, the stuff bits shall be inserted at
  fixed positions; they are called fixed stuff bits. There shall be a
  fixed stuff bit before the first bit of the stuff count, even if the
  last bits of the preceding field are a sequence of five consecutive
  bits of identical value, there shall be only the fixed stuff bit,
  there shall not be two consecutive stuff bits. A further fixed stuff
  bit shall be inserted after each fourth bit of the CRC field [...]

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
---
 include/linux/can/length.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 69336549d24f..b8c12c83bc51 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -72,17 +72,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
+#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
 
 /*
  * Size of a CAN-FD Extended Frame
@@ -101,17 +102,18 @@
  * Error Status Indicator (ESI)		1
  * Data length code (DLC)		4
  * Data field				0...512
- * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * Stuff Bit Count (SBC)		4
  * CRC					0...16: 17 20...64:21
  * CRC delimiter (CD)			1
+ * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
  * ACK slot (AS)			1
  * ACK delimiter (AD)			1
  * End-of-frame (EOF)			7
  * Inter frame spacing			3
  *
- * assuming CRC21, rounded up and ignoring bitstuffing
+ * assuming CRC21, rounded up and ignoring dynamic bitstuffing
  */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
+#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
 
 /*
  * Maximum size of a Classical CAN frame
-- 
2.39.3

[PATCH v5 2/3] can: length: fix description of the RRS field

[Vincent Mailhol]

The CAN-FD frames only have one reserved bit. The bit corresponding to
Classical CAN frame's RTR bit is called the "Remote Request
Substitution (RRS)" [1].

N.B. The RRS is not to be confused with the Substitute Remote Request
(SRR).

Fix the description in the CANFD_FRAME_OVERHEAD_SFF/EFF macros.

The total remains unchanged, so this is just a documentation fix.

In addition to the above add myself as copyright owner for 2020 (as
coauthor of the initial version, c.f. Fixes tag).

[1] ISO 11898-1:2015 paragraph 10.4.2.3 "Arbitration field":

  RSS bit [only in FD Frames]

    The RRS bit shall be transmitted in FD Frames at the position of
    the RTR bit in Classical Frames. The RRS bit shall be transmitted
    dominant, but receivers shall accept recessive and dominant RRS
    bits.

Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
---
 include/linux/can/length.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index b8c12c83bc51..521fdbce2d69 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
+ * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
@@ -64,7 +65,7 @@
  * ---------------------------------------------------------
  * Start-of-frame			1
  * Identifier				11
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Identifier extension bit (IDE)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
@@ -95,7 +96,7 @@
  * Substitute remote request (SRR)	1
  * Identifier extension bit (IDE)	1
  * Identifier B				18
- * Reserved bit (r1)			1
+ * Remote Request Substitution (RRS)	1
  * Flexible data rate format (FDF)	1
  * Reserved bit (r0)			1
  * Bit Rate Switch (BRS)		1
-- 
2.39.3

[PATCH v5 3/3] can: length: refactor frame lengths definition to add size in bits

[Vincent Mailhol]

Introduce a method to calculate the exact size in bits of a CAN(-FD)
frame with or without dynamic bitstuffing.

These are all the possible combinations taken into account:

  - Classical CAN or CAN-FD
  - Standard or Extended frame format
  - CAN-FD CRC17 or CRC21
  - Include or not intermission

Instead of doing several individual macro definitions, declare the
can_frame_bits() function-like macro. To this extent, do a full
refactoring of the length definitions.

In addition add the can_frame_bytes(). This function-like macro
replaces the existing macro:

  - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
  - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
  - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
  - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)

Function-like macros were chosen over inline functions because they
can be used to initialize const struct fields.

The different maximum frame lengths (maximum data length, including
intermission) are as follow:

   Frame type				bits	bytes
  -------------------------------------------------------
   Classic CAN SFF no bitstuffing	111	14
   Classic CAN EFF no bitstuffing	131	17
   Classic CAN SFF bitstuffing		135	17
   Classic CAN EFF bitstuffing		160	20
   CAN-FD SFF no bitstuffing		579	73
   CAN-FD EFF no bitstuffing		598	75
   CAN-FD SFF bitstuffing		712	89
   CAN-FD EFF bitstuffing		736	92

The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
can_frame_bytes(true, true, CANFD_MAX_DLEN).

In addition to the above:

 - Use ISO 11898-1:2015 definitions for the names of the CAN frame
   fields.
 - Include linux/bits.h for use of BITS_PER_BYTE.
 - Include linux/math.h for use of mult_frac() and
   DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
   patch, but the include was previously omitted.
 - Add copyright 2023 for myself.

Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
---
 drivers/net/can/dev/length.c |  15 +-
 include/linux/can/length.h   | 302 +++++++++++++++++++++++++----------
 2 files changed, 216 insertions(+), 101 deletions(-)

diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
index b48140b1102e..b7f4d76dd444 100644
--- a/drivers/net/can/dev/length.c
+++ b/drivers/net/can/dev/length.c
@@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
 	else
 		len = cf->len;
 
-	if (can_is_canfd_skb(skb)) {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CANFD_FRAME_OVERHEAD_EFF;
-		else
-			len += CANFD_FRAME_OVERHEAD_SFF;
-	} else {
-		if (cf->can_id & CAN_EFF_FLAG)
-			len += CAN_FRAME_OVERHEAD_EFF;
-		else
-			len += CAN_FRAME_OVERHEAD_SFF;
-	}
-
-	return len;
+	return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,
+			       false, len);
 }
 EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index 521fdbce2d69..abc978b38f79 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,132 +1,258 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
- * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
+ * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
  */
 
 #ifndef _CAN_LENGTH_H
 #define _CAN_LENGTH_H
 
+#include <linux/bits.h>
 #include <linux/can.h>
 #include <linux/can/netlink.h>
+#include <linux/math.h>
 
 /*
- * Size of a Classical CAN Standard Frame
+ * Size of a Classical CAN Standard Frame header in bits
  *
- * Name of Field			Bits
+ * Name of Field				Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote transmission request (RTR)	1
- * Identifier extension bit (IDE)	1
- * Reserved bit (r0)			1
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicator (FDF)		1
+ *	Data Length Code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CAN_FRAME_HEADER_SFF_BITS 19
+
+/*
+ * Size of a Classical CAN Extended Frame header in bits
  *
- * rounded up and ignoring bitstuffing
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Transmission Request (RTR)	1
+ * Control field:
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (r0)			1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
  */
-#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+#define CAN_FRAME_HEADER_EFF_BITS 39
 
 /*
- * Size of a Classical CAN Extended Frame
+ * Size of a CAN-FD Standard Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	IDentifier Extension bit (IDE)		1
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_SFF_BITS 22
+
+/*
+ * Size of a CAN-FD Extended Frame in bits
+ *
+ * Name of Field				Bits
+ * ---------------------------------------------------------
+ * Start Of Frame (SOF)				1
+ * Arbitration field:
+ *	base ID					11
+ *	Substitute Remote Request (SRR)		1
+ *	IDentifier Extension bit (IDE)		1
+ *	ID extension				18
+ *	Remote Request Substitution (RRS)	1
+ * Control field:
+ *	FD Format indicator (FDF)		1
+ *	Reserved bit (res)			1
+ *	Bit Rate Switch (BRS)			1
+ *	Error Status Indicator (ESI)		1
+ *	Data length code (DLC)			4
+ *
+ * including all fields preceding the data field, ignoring bitstuffing
+ */
+#define CANFD_FRAME_HEADER_EFF_BITS 41
+
+/*
+ * Size of a CAN CRC Field in bits
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote transmission request (RTR)	1
- * Reserved bits (r1, r0)		2
- * Data length code (DLC)		4
- * Data field				0...64
- * CRC					15
- * CRC delimiter			1
- * ACK slot				1
- * ACK delimiter			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
+ * CRC sequence (CRC15)			15
+ * CRC Delimiter			1
+ *
+ * ignoring bitstuffing
+ */
+#define CAN_FRAME_CRC_FIELD_BITS 16
+
+/*
+ * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
  *
- * rounded up and ignoring bitstuffing
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Stuff Count				4
+ * CRC Sequence (CRC17)			17
+ * CRC Delimiter			1
+ * Fixed stuff bits			6
  */
-#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+#define CANFD_FRAME_CRC17_FIELD_BITS 28
 
 /*
- * Size of a CAN-FD Standard Frame
+ * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier				11
- * Remote Request Substitution (RRS)	1
- * Identifier extension bit (IDE)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
- */
-#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
+ * Stuff Count				4
+ * CRC sequence (CRC21)			21
+ * CRC Delimiter			1
+ * Fixed stuff bits			7
+ */
+#define CANFD_FRAME_CRC21_FIELD_BITS 33
 
 /*
- * Size of a CAN-FD Extended Frame
+ * Size of a CAN(-FD) Frame footer in bits
  *
  * Name of Field			Bits
  * ---------------------------------------------------------
- * Start-of-frame			1
- * Identifier A				11
- * Substitute remote request (SRR)	1
- * Identifier extension bit (IDE)	1
- * Identifier B				18
- * Remote Request Substitution (RRS)	1
- * Flexible data rate format (FDF)	1
- * Reserved bit (r0)			1
- * Bit Rate Switch (BRS)		1
- * Error Status Indicator (ESI)		1
- * Data length code (DLC)		4
- * Data field				0...512
- * Stuff Bit Count (SBC)		4
- * CRC					0...16: 17 20...64:21
- * CRC delimiter (CD)			1
- * Fixed Stuff bits (FSB)		0...16: 6 20...64:7
- * ACK slot (AS)			1
- * ACK delimiter (AD)			1
- * End-of-frame (EOF)			7
- * Inter frame spacing			3
- *
- * assuming CRC21, rounded up and ignoring dynamic bitstuffing
- */
-#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
+ * ACK slot				1
+ * ACK delimiter			1
+ * End Of Frame (EOF)			7
+ *
+ * including all fields following the CRC field
+ */
+#define CAN_FRAME_FOOTER_BITS 9
+
+/*
+ * First part of the Inter Frame Space
+ * (a.k.a. IMF - intermission field)
+ */
+#define CAN_INTERMISSION_BITS 3
+
+/**
+ * can_bitstuffing_len() - Calculate the maximum length with bitstuffing
+ * @destuffed_len: length of a destuffed bit stream
+ *
+ * The worst bit stuffing case is a sequence in which dominant and
+ * recessive bits alternate every four bits:
+ *
+ *   Destuffed: 1 1111  0000  1111  0000  1111
+ *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
+ *
+ * Nomenclature
+ *
+ *  - "0": dominant bit
+ *  - "o": dominant stuff bit
+ *  - "1": recessive bit
+ *  - "i": recessive stuff bit
+ *
+ * Aside from the first bit, one stuff bit is added every four bits.
+ *
+ * Return: length of the stuffed bit stream in the worst case scenario.
+ */
+#define can_bitstuffing_len(destuffed_len)			\
+	(destuffed_len + (destuffed_len - 1) / 4)
+
+#define __can_bitstuffing_len(bitstuffing, destuffed_len)	\
+	(bitstuffing ? can_bitstuffing_len(destuffed_len) :	\
+		       destuffed_len)
+
+#define __can_cc_frame_bits(is_eff, bitstuffing,		\
+			    intermission, data_len)		\
+(								\
+	__can_bitstuffing_len(bitstuffing,			\
+		(is_eff ? CAN_FRAME_HEADER_EFF_BITS :		\
+			  CAN_FRAME_HEADER_SFF_BITS) +		\
+		(data_len) * BITS_PER_BYTE +			\
+		CAN_FRAME_CRC_FIELD_BITS) +			\
+	CAN_FRAME_FOOTER_BITS +					\
+	(intermission ? CAN_INTERMISSION_BITS : 0)		\
+)
+
+#define __can_fd_frame_bits(is_eff, bitstuffing,		\
+			    intermission, data_len)		\
+(								\
+	__can_bitstuffing_len(bitstuffing,			\
+		(is_eff ? CANFD_FRAME_HEADER_EFF_BITS :		\
+			  CANFD_FRAME_HEADER_SFF_BITS) +	\
+		(data_len) * BITS_PER_BYTE) +			\
+	((data_len) <= 16 ?					\
+		CANFD_FRAME_CRC17_FIELD_BITS :			\
+		CANFD_FRAME_CRC21_FIELD_BITS) +			\
+	CAN_FRAME_FOOTER_BITS +					\
+	(intermission ? CAN_INTERMISSION_BITS : 0)		\
+)
+
+/**
+ * can_frame_bits() - Calculate the number of bits on the wire in a
+ *	CAN frame
+ * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
+ * @is_eff: true: Extended frame; false: Standard frame.
+ * @bitstuffing: true: calculate the bitstuffing worst case; false:
+ *	calculate the bitstuffing best case (no dynamic
+ *	bitstuffing). CAN-FD's fixed stuff bits are always included.
+ * @intermission: if and only if true, include the inter frame space
+ *	assuming no bus idle (i.e. only the intermission). Strictly
+ *	speaking, the inter frame space is not part of the
+ *	frame. However, it is needed when calculating the delay
+ *	between the Start Of Frame of two consecutive frames.
+ * @data_len: length of the data field in bytes. Correspond to
+ *	can(fd)_frame->len. Should be zero for remote frames. No
+ *	sanitization is done on @data_len and it shall have no side
+ *	effects.
+ *
+ * Return: the numbers of bits on the wire of a CAN frame.
+ */
+#define can_frame_bits(is_fd, is_eff, bitstuffing,		\
+		       intermission, data_len)			\
+(								\
+	is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,	\
+				    intermission, data_len) :	\
+		__can_cc_frame_bits(is_eff, bitstuffing,	\
+				    intermission, data_len)	\
+)
+
+/*
+ * Number of bytes in a CAN frame
+ * (rounded up, including intermission)
+ */
+#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)	\
+	DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing,	\
+				    true, data_len),		\
+		     BITS_PER_BYTE)
 
 /*
  * Maximum size of a Classical CAN frame
- * (rounded up and ignoring bitstuffing)
+ * (rounded up, ignoring bitstuffing but including intermission)
  */
-#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)
+#define CAN_FRAME_LEN_MAX can_frame_bytes(false, true, false, CAN_MAX_DLEN)
 
 /*
  * Maximum size of a CAN-FD frame
- * (rounded up and ignoring bitstuffing)
+ * (rounded up, ignoring dynamic bitstuffing but including intermission)
  */
-#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)
+#define CANFD_FRAME_LEN_MAX can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
 
 /*
  * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
-- 
2.39.3