[PATCH linux-next v2 01/14] mtd: spi-nor: remove micron_quad_enable()

[PATCH linux-next v2 01/14] mtd: spi-nor: remove micron_quad_enable()

[Cyrille Pitchen]

Le 20/01/2016 06:13, Bean Huo ??? (beanhuo) a ?crit :
>> Message-ID:
>> 	<6177f7317fe11922e1d1b6dc4548afbaf0ccebdd.1452268345.git.cyrille.
>> pitchen at atmel.com>
>>
>> Content-Type: text/plain
>>
>> This patch remove the micron_quad_enable() function which force the Quad
>> SPI mode. However, once this mode is enabled, the Micron memory expect
>> ALL
>> commands to use the SPI 4-4-4 protocol. Hence a failure does occur when
>> calling spi_nor_wait_till_ready() right after the update of the Enhanced
>> Volatile Configuration Register (EVCR) in the micron_quad_enable() as
>> the SPI controller driver is not aware about the protocol change.
>> Since there is almost no performance increase using Fast Read 4-4-4
>> commands instead of Fast Read 1-1-4 commands, we rather keep on using
>> the
>> Extended SPI mode than enabling the Quad SPI mode.
>>
>> Let's take the example of the pretty standard use of 8 dummy cycles during
>> Fast Read operations on 64KB erase sectors:
>>
>> Fast Read 1-1-4 requires 8 cycles for the command, then 24 cycles for the
>> 3byte address followed by 8 dummy clock cycles and finally 65536*2 cycles
>> for the read data; so 131112 clock cycles.
>>
>> On the other hand the Fast Read 4-4-4 would require 2 cycles for the
>> command, then 6 cycles for the 3byte address followed by 8 dummy clock
>> cycles and finally 65536*2 cycles for the read data. So 131088 clock
>> cycles. The theorical bandwidth increase is 0.0%.
>>
>> Now using Fast Read operations on 512byte pages:
>> Fast Read 1-1-4 needs 8+24+8+(512*2) = 1064 clock cycles whereas Fast
>> Read 4-4-4 would requires 2+6+8+(512*2) = 1040 clock cycles. Hence the
>> theorical bandwidth increase is 2.3%.
>> Consecutive reads for non sequential pages is not a relevant use case so
>> The Quad SPI mode is not worth it.
>>
>> mtd_speedtest seems to confirm these figures.
>>
>> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
>> Fixes: 548cd3ab54da ("mtd: spi-nor: Add quad I/O support for Micron SPI
>> NOR")
>> ---
>>  drivers/mtd/spi-nor/spi-nor.c | 46 +------------------------------------------
>>  1 file changed, 1 insertion(+), 45 deletions(-)
>>
>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>> index ed0c19c558b5..3028c06547c1 100644
>> --- a/drivers/mtd/spi-nor/spi-nor.c
>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>> @@ -1100,45 +1100,6 @@ static int spansion_quad_enable(struct spi_nor
>> *nor)
>>  	return 0;
>>  }
>>
>> -static int micron_quad_enable(struct spi_nor *nor)
>> -{
>> -	int ret;
>> -	u8 val;
>> -
>> -	ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
>> -	if (ret < 0) {
>> -		dev_err(nor->dev, "error %d reading EVCR\n", ret);
>> -		return ret;
>> -	}
>> -
>> -	write_enable(nor);
>> -
>> -	/* set EVCR, enable quad I/O */
>> -	nor->cmd_buf[0] = val & ~EVCR_QUAD_EN_MICRON;
>> -	ret = nor->write_reg(nor, SPINOR_OP_WD_EVCR, nor->cmd_buf, 1);
>> -	if (ret < 0) {
>> -		dev_err(nor->dev, "error while writing EVCR register\n");
>> -		return ret;
>> -	}
>> -
>> -	ret = spi_nor_wait_till_ready(nor);
>> -	if (ret)
>> -		return ret;
>> -
>> -	/* read EVCR and check it */
>> -	ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
>> -	if (ret < 0) {
>> -		dev_err(nor->dev, "error %d reading EVCR\n", ret);
>> -		return ret;
>> -	}
>> -	if (val & EVCR_QUAD_EN_MICRON) {
>> -		dev_err(nor->dev, "Micron EVCR Quad bit not clear\n");
>> -		return -EINVAL;
>> -	}
>> -
>> -	return 0;
>> -}
>> -
>>  static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
>>  {
>>  	int status;
>> @@ -1152,12 +1113,7 @@ static int set_quad_mode(struct spi_nor *nor,
>> const struct flash_info *info)
>>  		}
>>  		return status;
>>  	case SNOR_MFR_MICRON:
>> -		status = micron_quad_enable(nor);
>> -		if (status) {
>> -			dev_err(nor->dev, "Micron quad-read not enabled\n");
>> -			return -EINVAL;
>> -		}
>> -		return status;
>> +		return 0;
>>  	default:
>>  		status = spansion_quad_enable(nor);
>>  		if (status) {
>> --
>> 1.8.2.2
>>
>>
>>
>>
> 
> Hi, Cyrlle
> Micron_quad_enable() function is just for how to enable Micron spi nor Quad mode,
> does not force to use SPI nor quad mode. if does not need SPI NOR quad mode,
> why spi-nor.c need set_quad_mode(), according to your patch, this function also need to
> be removed?
> Another question, if there is user want to enable SPI nor quad mode, how to do?
> 

Hi Bean,

the set_quad_mode() function should not been removed from spi-nor.c as it is
needed for both Macronix and Spansion memories.
Indeed, what macronix_quad_enable() and spansion_quad_enable() do is to change
a dedicated bit in some status/configuration register to enable Quad SPI
operations. More precisely, this disables some features such as the Write
Protection (Spansion & Macronix) or the Reset (Macronix) / Hold (Spansion) so
the associated pins can be reassigned to IO2 and IO3 data lines... and that's
all!
What I mean is that once set_quad_mode() has been called, Macronix and Spansion
memories still reply to commands such as Read Status Register in protocol
SPI 1-1-1. Of course, they now also support Fast Read 1-1-4 (0x6b) or 1-4-4
(0xeb).
For Macronix memories, setting the Quad Enable bit in its Status Register is
NOT the same as entering its QPI mode. In QPI mode, ALL commands are expected
to use the SPI 4-4-4 protocol: this mode is not used by spi-nor.c

Then going back to the Micron case, micron_quad_enable() makes the memory
enter its Quad mode where ALL commands must use the SPI 4-4-4 protocol. So
it is definitely not the same thing as what either macronix_quad_enable() or
spansion_quad_enable() do.

Also the current code of micron_quad_enable() is broken:

[...]
Here, the memory still expects the SPI 1-1-1 to be used by write_reg() or
read_reg().

	/* set EVCR, enable quad I/O */
	nor->cmd_buf[0] = val & ~EVCR_QUAD_EN_MICRON;
	ret = nor->write_reg(nor, SPINOR_OP_WD_EVCR, nor->cmd_buf, 1);
	if (ret < 0) {
		dev_err(nor->dev, "error while writing EVCR register\n");
		return ret;
	}

However, once the Quad Enable bit has been cleared into the Enhanced Volatile
Configuration Register, all commands must use the SPI 4-4-4 protocol.
Especially, the later call of spi_nor_wait_till_ready(), which calls read_reg()
to read the Status Register, will fail because the QSPI controller has to mean
to know about the protocol switch hence keeps on sending the Read Status
Register command with the wrong SPI 1-1-1 protocol.
This is the issue I faced when using a Micron memory with the Atmel QSPI
controller embedded in a sama5d2 SoC. Also for the same reason, users of the
m25p80 driver won't be able to use Micron memories for QSPI operations too.

	ret = spi_nor_wait_till_ready(nor);
	if (ret)
		return ret;
[...]

So in its current state, micron_quad_enable() prevents us from using Micron
memories for Quad SPI operations. Some code is missing to make it work.



As I said in the patch description, using the SPI 4-4-4 protocol is not
relevant for MTD usage. It would be worth for XIP operations but this is not the
purpose of the spi-nor driver.
Also, the series of patches still support the Micron Quad SPI mode: the spi-nor
driver no longer enables this mode itself but it still can adapt itself whether
the Quad SPI mode had already been enabled by a previous bootloader or at
reset. This is the purpose of the patch focusing on Read JEDEC ID commands:
it is used to probe the current state of the memory and use the SPI 4-4-4 if
needed.

Best regards,

Cyrille

[PATCH linux-next v2 01/14] mtd: spi-nor: remove micron_quad_enable()

[Brian Norris]

On Wed, Feb 03, 2016 at 12:16:53PM +0100, Cyrille Pitchen wrote:

> So in its current state, micron_quad_enable() prevents us from using Micron
> memories for Quad SPI operations. Some code is missing to make it work.

TL;DR: the original code adding micron_quad_enable() was broken and
should never have been merged (sorry, my bad). Next time, please test
your changes Bean.

> As I said in the patch description, using the SPI 4-4-4 protocol is not
> relevant for MTD usage. It would be worth for XIP operations but this is not the
> purpose of the spi-nor driver.

I'm not completely opposed to using it, if someone can support it well,
test it, and prove it actually provides real benefits. But none of the
above have been satisfied yet.

Regards,
Brian

[PATCH linux-next v2 00/14] mtd: spi-nor: add driver for Atmel QSPI controller

[Cyrille Pitchen]

Hi all,

This series of patches adds support to the Atmel QSPI controller available
on sama5d2 SoCs. It was tested on a sama5d2 xplained ultra board with a 
Micron n25q128a13 QSPI memory and a at25df321a SPI memory.

In order to use the Micron memory in its Quad SPI mode, the spi-nor
framework needed to be patched to fix the support of Quad/Dual SPI
protocols with some memory manufacturers such as Spansion, Micron and
Macronix. There are many comments in the source code to explain the
implementation choices based on the datasheets from memory manufacturers.


This series was based and tested on linux-next

1 - Atmel QSPI + Micron n25q128a13 (atmel-quadspi.c driver)

SPI 1-1-1: This mode was tested replacing SPI_NOR_QUAD by SPI_NOR_FAST as
           argument to spi_nor_scan() called from atmel_qspi_probe().

SPI 1-1-4: Bootloaders (at91bootstrap/uboot) don't enable the Quad SPI
           mode of the Micron memory. When probed from Linux, the memory
           uses its Extended SPI mode and replies to the regular Read ID
           (0x9f) command.

SPI 4-4-4: The romcode enabled the Quad SPI mode the of Micron memory
           before loading the at91bootstrap. When probed from Linux, the
           memory uses its Quad SPI mode and no longer replies to the
           regular Read ID (0x9f) command but instead to the Read ID
           Multiple I/O (0xaf) command. The memory expects ALL commands
           to use the SPI 4-4-4 protocol.

2 - Atmel QSPI + Spansion s25fl512 (atmel-quadspi.c driver)

SPI 1-1-4: default settings. Early developpements on a FPGA board.

3 - Atmel SPI + at25df321a (m25p80.c driver)

SPI 1-1-1: tested with the m25p80 driver for non regression purpose.


Winbond and Macronix memories were NOT tested. The patches were written
only based on the manufacturers' datasheets.


Best regards,

Cyrille


ChangeLog:

v1 -> v2:
- I've totally reworked the whole series. Especially I have split the
  former patch 2 to ease the code review. The Single/Dual/Quad SPI mode
  support fixes are now done by manufacturer.
- fix support and probing of Winbond memories.
- m25p80: compute the number of dummy bytes from both the number of dummy
  clock cycles and the number of I/O lines used to send them.
- fix Kconfig dependencies for the Atmel QSPI controller driver (it should
  fix the kbuild test robot warnings).
- add more comments.


Cyrille Pitchen (14):
  mtd: spi-nor: remove micron_quad_enable()
  mtd: spi-nor: properly detect the memory when it boots in Quad or Dual
    mode
  mtd: spi-nor: select op codes and SPI NOR protocols by manufacturer
  mtd: spi-nor: fix support of Macronix memories
  mtd: spi-nor: fix support of Winbond memories
  mtd: spi-nor: fix support of Micron memories
  mtd: spi-nor: fix support of Spansion memories
  mtd: spi-nor: configure the number of dummy clock cycles by
    manufacturer
  mtd: spi-nor: configure the number of dummy clock cycles on Micron
    memories
  mtd: spi-nor: configure the number of dummy clock cycles on Macronix
    memories
  mtd: spi-nor: configure the number of dummy clock cycles on Spansion
    memories
  mtd: m25p80: add support of dual and quad spi protocols to all
    commands
  Documentation: atmel-quadspi: add binding file for Atmel QSPI driver
  mtd: atmel-quadspi: add driver for Atmel QSPI controller

 .../devicetree/bindings/mtd/atmel-quadspi.txt      |  32 +
 drivers/mtd/devices/m25p80.c                       | 192 ++++-
 drivers/mtd/spi-nor/Kconfig                        |   9 +
 drivers/mtd/spi-nor/Makefile                       |   1 +
 drivers/mtd/spi-nor/atmel-quadspi.c                | 877 +++++++++++++++++++
 drivers/mtd/spi-nor/spi-nor.c                      | 928 +++++++++++++++++++--
 include/linux/mtd/spi-nor.h                        |  71 +-
 7 files changed, 1985 insertions(+), 125 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/mtd/atmel-quadspi.txt
 create mode 100644 drivers/mtd/spi-nor/atmel-quadspi.c

-- 
1.8.2.2

[PATCH linux-next v2 01/14] mtd: spi-nor: remove micron_quad_enable()

[Cyrille Pitchen]

This patch remove the micron_quad_enable() function which force the Quad
SPI mode. However, once this mode is enabled, the Micron memory expect ALL
commands to use the SPI 4-4-4 protocol. Hence a failure does occur when
calling spi_nor_wait_till_ready() right after the update of the Enhanced
Volatile Configuration Register (EVCR) in the micron_quad_enable() as
the SPI controller driver is not aware about the protocol change.

Since there is almost no performance increase using Fast Read 4-4-4
commands instead of Fast Read 1-1-4 commands, we rather keep on using the
Extended SPI mode than enabling the Quad SPI mode.

Let's take the example of the pretty standard use of 8 dummy cycles during
Fast Read operations on 64KB erase sectors:

Fast Read 1-1-4 requires 8 cycles for the command, then 24 cycles for the
3byte address followed by 8 dummy clock cycles and finally 65536*2 cycles
for the read data; so 131112 clock cycles.

On the other hand the Fast Read 4-4-4 would require 2 cycles for the
command, then 6 cycles for the 3byte address followed by 8 dummy clock
cycles and finally 65536*2 cycles for the read data. So 131088 clock
cycles. The theorical bandwidth increase is 0.0%.

Now using Fast Read operations on 512byte pages:
Fast Read 1-1-4 needs 8+24+8+(512*2) = 1064 clock cycles whereas Fast
Read 4-4-4 would requires 2+6+8+(512*2) = 1040 clock cycles. Hence the
theorical bandwidth increase is 2.3%.
Consecutive reads for non sequential pages is not a relevant use case so
The Quad SPI mode is not worth it.

mtd_speedtest seems to confirm these figures.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Fixes: 548cd3ab54da ("mtd: spi-nor: Add quad I/O support for Micron SPI NOR")
---
 drivers/mtd/spi-nor/spi-nor.c | 46 +------------------------------------------
 1 file changed, 1 insertion(+), 45 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index ed0c19c558b5..3028c06547c1 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1100,45 +1100,6 @@ static int spansion_quad_enable(struct spi_nor *nor)
 	return 0;
 }
 
-static int micron_quad_enable(struct spi_nor *nor)
-{
-	int ret;
-	u8 val;
-
-	ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
-	if (ret < 0) {
-		dev_err(nor->dev, "error %d reading EVCR\n", ret);
-		return ret;
-	}
-
-	write_enable(nor);
-
-	/* set EVCR, enable quad I/O */
-	nor->cmd_buf[0] = val & ~EVCR_QUAD_EN_MICRON;
-	ret = nor->write_reg(nor, SPINOR_OP_WD_EVCR, nor->cmd_buf, 1);
-	if (ret < 0) {
-		dev_err(nor->dev, "error while writing EVCR register\n");
-		return ret;
-	}
-
-	ret = spi_nor_wait_till_ready(nor);
-	if (ret)
-		return ret;
-
-	/* read EVCR and check it */
-	ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
-	if (ret < 0) {
-		dev_err(nor->dev, "error %d reading EVCR\n", ret);
-		return ret;
-	}
-	if (val & EVCR_QUAD_EN_MICRON) {
-		dev_err(nor->dev, "Micron EVCR Quad bit not clear\n");
-		return -EINVAL;
-	}
-
-	return 0;
-}
-
 static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
 {
 	int status;
@@ -1152,12 +1113,7 @@ static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
 		}
 		return status;
 	case SNOR_MFR_MICRON:
-		status = micron_quad_enable(nor);
-		if (status) {
-			dev_err(nor->dev, "Micron quad-read not enabled\n");
-			return -EINVAL;
-		}
-		return status;
+		return 0;
 	default:
 		status = spansion_quad_enable(nor);
 		if (status) {
-- 
1.8.2.2