Re: [PATCH v4 2/3] mtd: cfi_cmdset_0002: Use chip_ready() for write on S29GL064N

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Vignesh,

On 17.03.22 11:01, Vignesh Raghavendra wrote:
> 
> 
> On 16/03/22 10:51 pm, Miquel Raynal wrote:
>> Hi Tokunori,
>>
>> ikegami.t@gmail.com wrote on Thu, 17 Mar 2022 00:54:54 +0900:
>>
>>> As pointed out by this bug report [1], buffered writes are now broken on
>>> S29GL064N. This issue comes from a rework which switched from using chip_good()
>>> to chip_ready(), because DQ true data 0xFF is read on S29GL064N and an error
>>> returned by chip_good().
>>
>> Vignesh, I believe you understand this issue better than I do, can you
>> propose an improved commit log?
> 
> How about:
> 
> Since commit dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
> check correct value") buffered writes fail on S29GL064N. This is
> because, on S29GL064N, reads return 0xFF at the end of DQ polling for
> write completion, where as, chip_good() check expects actual data
> written to the last location to be returned post DQ polling completion.
> Fix is to revert to using chip_good() for S29GL064N which only checks
> for DQ lines to settle down to determine write completion.

Message sounds good to me with one remark: The issue is independent of
whether buffered writes are used or not. It's just because buffered writes
are the default, that it was broken by dfeae1073583 ("mtd: cfi_cmdset_0002:
Change write buffer to check correct value"). The word write case was broken
by 37c673ade35c ("mtd: cfi_cmdset_0002: Use chip_good() to retry in
do_write_oneword()"), so the commit message should probably reference
both. as this commit indeed fixes both FORCE_WORD_WRITE == 0 and == 1.

Thanks,
Ahmad


> 
>>
>>> One way to solve the issue is to revert the change
>>> partially to use chip_ready for S29GL064N.
>>>
>>> [1] https://lore.kernel.org/r/b687c259-6413-26c9-d4c9-b3afa69ea124@pengutronix.de/
>>>
>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to check correct value")
>>> Signed-off-by: Tokunori Ikegami <ikegami.t@gmail.com>
>>> Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
>>> Cc: stable@vger.kernel.org
>>> ---
>>>  drivers/mtd/chips/cfi_cmdset_0002.c | 25 +++++++++++++++++++++----
>>>  1 file changed, 21 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c
>>> index e68ddf0f7fc0..6c57f85e1b8e 100644
>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
>>> @@ -866,6 +866,23 @@ static int __xipram chip_check(struct map_info *map, struct flchip *chip,
>>>  		chip_check(map, chip, addr, &datum); \
>>>  	})
>>>  
>>> +static bool __xipram cfi_use_chip_ready_for_write(struct map_info *map)
>>
>> At the very least I would call this function:
>> cfi_use_chip_ready_for_writes()
>>
>> Yet, I still don't fully get what chip_ready is versus chip_good.
>>
>>> +{
>>> +	struct cfi_private *cfi = map->fldrv_priv;
>>> +
>>> +	return cfi->mfr == CFI_MFR_AMD && cfi->id == 0x0c01;
>>> +}
>>> +
>>> +static int __xipram chip_good_for_write(struct map_info *map,
>>> +					struct flchip *chip, unsigned long addr,
>>> +					map_word expected)
>>> +{
>>> +	if (cfi_use_chip_ready_for_write(map))
>>> +		return chip_ready(map, chip, addr);
>>
>> If possible and not too invasive I would definitely add a "quirks" flag
>> somewhere instead of this cfi_use_chip_ready_for_write() check.
>>
>> Anyway, I would move this to the chip_good() implementation directly so
>> we partially hide the quirks complexity from the core.
> 
> Yeah, unfortunately this driver does not use quirk flags and tends to
> hide quirks behind bool functions like above
> 
> Regards
> Vignesh
> 


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