[RFC PATCH v2 2/3] iplink_can: canxl: support Remote Request Substitution bit access

[Oliver Hartkopp <socketcan@hartkopp.net>]

The Remote Request Substitution bit is a dominant bit ("0") in the CAN XL
frame. As some CAN XL controllers support to access this bit a new
CANXL_RRS value has been defined for the canxl_frame.flags element.

To read/write the Remote Request Substitution (RRS) bit in the CAN XL
frame the CAN_CTRLMODE_XL_RRS has to be enabled in CAN driver.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 include/uapi/linux/can.h         | 5 ++++-
 include/uapi/linux/can/netlink.h | 1 +
 ip/iplink_can.c                  | 6 ++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index 229a77ff..513d3d75 100644
--- a/include/uapi/linux/can.h
+++ b/include/uapi/linux/can.h
@@ -180,20 +180,23 @@ struct canfd_frame {
 };
 
 /*
  * defined bits for canxl_frame.flags
  *
- * The canxl_frame.flags element contains two bits CANXL_XLF and CANXL_SEC
+ * The canxl_frame.flags element contains three bits CANXL_[XLF|SEC|RRS]
  * and shares the relative position of the struct can[fd]_frame.len element.
  * The CANXL_XLF bit ALWAYS needs to be set to indicate a valid CAN XL frame.
  * As a side effect setting this bit intentionally breaks the length checks
  * for Classical CAN and CAN FD frames.
+ * To read/write the Remote Request Substitution (RRS) bit in the CAN XL
+ * frame the CAN_CTRLMODE_XL_RRS has to be enabled in CAN driver.
  *
  * Undefined bits in canxl_frame.flags are reserved and shall be set to zero.
  */
 #define CANXL_XLF 0x80 /* mandatory CAN XL frame flag (must always be set!) */
 #define CANXL_SEC 0x01 /* Simple Extended Content (security/segmentation) */
+#define CANXL_RRS 0x02 /* Remote Request Substitution */
 
 /* the 8-bit VCID is optionally placed in the canxl_frame.prio element */
 #define CANXL_VCID_OFFSET 16 /* bit offset of VCID in prio element */
 #define CANXL_VCID_VAL_MASK 0xFFUL /* VCID is an 8-bit value */
 #define CANXL_VCID_MASK (CANXL_VCID_VAL_MASK << CANXL_VCID_OFFSET)
diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
index 416e2feb..19267678 100644
--- a/include/uapi/linux/can/netlink.h
+++ b/include/uapi/linux/can/netlink.h
@@ -104,10 +104,11 @@ struct can_ctrlmode {
 #define CAN_CTRLMODE_TDC_AUTO		0x200	/* FD transceiver automatically calculates TDCV */
 #define CAN_CTRLMODE_TDC_MANUAL		0x400	/* FD TDCV is manually set up by user */
 #define CAN_CTRLMODE_XL			0x800	/* CAN XL mode */
 #define CAN_CTRLMODE_XL_TDC_AUTO	0x1000	/* XL transceiver automatically calculates TDCV */
 #define CAN_CTRLMODE_XL_TDC_MANUAL	0x2000	/* XL TDCV is manually set up by user */
+#define CAN_CTRLMODE_XL_RRS		0x4000	/* XL enable RRS bit access */
 
 /*
  * CAN device statistics
  */
 struct can_device_stats {
diff --git a/ip/iplink_can.c b/ip/iplink_can.c
index 8dc9229b..9fe9ae6c 100644
--- a/ip/iplink_can.c
+++ b/ip/iplink_can.c
@@ -40,10 +40,11 @@ static void print_usage(FILE *f)
 		"\t[ presume-ack { on | off } ]\n"
 		"\t[ cc-len8-dlc { on | off } ]\n"
 		"\t[ tdc-mode { auto | manual | off } ]\n"
 		"\t[ xl { on | off } ]\n"
 		"\t[ xtdc-mode { auto | manual | off } ]\n"
+		"\t[ xlrrs { on | off } ]\n"
 		"\n"
 		"\t[ restart-ms TIME-MS ]\n"
 		"\t[ restart ]\n"
 		"\n"
 		"\t[ termination { 0..65535 } ]\n"
@@ -123,10 +124,11 @@ static void print_ctrlmode(enum output_type t, __u32 flags, const char* key)
 	print_flag(t, &flags, CAN_CTRLMODE_TDC_AUTO, "TDC-AUTO");
 	print_flag(t, &flags, CAN_CTRLMODE_TDC_MANUAL, "TDC-MANUAL");
 	print_flag(t, &flags, CAN_CTRLMODE_XL, "XL");
 	print_flag(t, &flags, CAN_CTRLMODE_XL_TDC_AUTO, "XL-TDC-AUTO");
 	print_flag(t, &flags, CAN_CTRLMODE_XL_TDC_MANUAL, "XL-TDC-MANUAL");
+	print_flag(t, &flags, CAN_CTRLMODE_XL_RRS, "XL-RRS");
 
 	if (flags)
 		print_hex(t, NULL, "%x", flags);
 
 	close_json_array(t, "> ");
@@ -333,10 +335,14 @@ static int can_parse_opt(struct link_util *lu, int argc, char **argv,
 					   CAN_CTRLMODE_XL_TDC_MANUAL;
 			} else {
 				invarg("\"xtdc-mode\" must be either of \"auto\", \"manual\" or \"off\"",
 					*argv);
 			}
+		} else if (matches(*argv, "xlrrs") == 0) {
+			NEXT_ARG();
+			set_ctrlmode("xlrrs", *argv, &cm,
+				     CAN_CTRLMODE_XL_RRS);
 		} else if (matches(*argv, "restart") == 0) {
 			__u32 val = 1;
 
 			addattr32(n, 1024, IFLA_CAN_RESTART, val);
 		} else if (matches(*argv, "restart-ms") == 0) {
-- 
2.45.2