linux-kernel - Re: [BUG] mtd: cfi_cmdset_0002: write regression since v4.17-rc1

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Message-ID: <08c76c86-c015-28c3-47b5-18d8e50258e9@gmail.com>
Date:   Wed, 9 Mar 2022 01:40:33 +0900
From:   Tokunori Ikegami <ikegami.t@...il.com>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        linux-mtd@...ts.infradead.org, Joakim.Tjernlund@...inera.com,
        miquel.raynal@...tlin.com, vigneshr@...com, richard@....at,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Cc:     Chris Packham <chris.packham@...iedtelesis.co.nz>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>, marek.vasut@...il.com,
        cyrille.pitchen@...ev4u.fr,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [BUG] mtd: cfi_cmdset_0002: write regression since v4.17-rc1

Hi,

On 2022/03/09 1:23, Ahmad Fatoum wrote:
> Hello Tokunori-san,
>
> On 08.03.22 17:13, Tokunori Ikegami wrote:
>> Hi Ahmad-san,
>>
>> On 2022/03/08 18:44, Ahmad Fatoum wrote:
>>> Hello Tokunori,
>>>
>>> On 06.03.22 16:49, Tokunori Ikegami wrote:
>>>> Hi,
>>>>
>>>> On 2022/03/04 20:11, Ahmad Fatoum wrote:
>>>>> Hello Tokunori-san,
>>>>>
>>>>> On 20.02.22 13:22, Tokunori Ikegami wrote:
>>>>>> Hi Ahmad-san,
>>>>>>
>>>>>> Could you please try the version 2 patch attached for the error case?
>>>>>> This version is to check the DQ true data 0xFF by chip_good().
>>>>> I had a similar patch locally as well at first. I just tested yours
>>>>> and I can't reproduce the issue.
>>>> Thanks for your support.
>>>> Sorry if possible could you please retest the attached the patch again since this fixed the version 1 patch maintainer review comments?
>>> Works good.
>>>
>>> Tested-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
>> Thank you so much for your test.
>>>>>> But I am not sure if this works or not since the error is possible to be caused by Hi-Z 0xff on floating bus or etc.
>>>>> That it works for me could be because of Hi-Z 0xff, which is why
>>>>> decided against it.
>>>> I see.
>>>>>>>>>> What seems to work for me is checking if chip_good or chip_ready
>>>>>>>>>> and map_word is equal to 0xFF. I can't justify why this is ok though.
>>>>>>>>>> (Worst case bus is floating at this point of time and Hi-Z is read
>>>>>>>>>> as 0xff on CPU data lines...)
>>>>>>>>> Sorry I am not sure about this.
>>>>>>>>> I thought the chip_ready() itself is correct as implemented as the data sheet in the past.
>>>>>>>>> But it did not work correctly so changed to use chip_good() instead as it is also correct.
>>>>>>>> What exactly in the datasheet makes you believe chip_good is not appropriate?
>>>>>>> I just mentioned about the actual issue behaviors as not worked chip_good() on S29GL964N and not worked chip_ready() on MX29GL512FHT2I-11G before etc.
>>>>>>> Anyway let me recheck the data sheet details as just checked it again quickly but needed more investigation to understand.
>>>>>> As far as I checked still both chip_good() and chip_ready() seem correct but still the root cause is unknown.
>>>>>> If as you mentioned the issue was cased by the DQ true data 0xFF I am not sure why the read work without any error after the write operation.
>>>>>> Also if the error was caused by the Hi-Z 0xff on floating bus as mentioned I am not sure why the read work without any error after the write operation with chip_ready().
>>>>>> Sorry anyway the root cause is also unknown when the write operation was changed to use chip_good() instead of chip_ready().
>>>>> I've be ok with v1 then. Restores working behavior for me and shouldn't break others.
>>>> Noted but still I am thinking the version 2 patch to check 0xff seems better than to use chip_ready() so let me consider this again later.
>>> The original version has less room for surprise as it restores previously
>>> working behavior. Assuming 0xFF to be good without backing from documentation
>>> is more risky IMO.
>> The change to check 0xFF can be limited for the S29GL064N chip do you have any comment about this?
> I see that, but I am not sure it's the correct thing to do on the S29GL064N,
> even if it seems to work. In absence of definitive information from the vendor,
> I'd prefer we just restore behavior as it was before, i.e. using chip_ready
> instead of chip_good for S29GL064N. This is the way of least surprise.

Thanks for your comment. I see okay I will keep the version patch 2 
reverting to use chip_ready() for S29GL064N under the review without the 
change to check 0xFF.

Regards,
Ikegami

>
>> Just attached the patch changed as so and thinking to send the patch as version 3 to the maintainer if you are okay.
>>
>> Regards,
>> Ikegami
>>
>>> Thanks for your continued support,
>>> Ahmad
>>>
>>>> Regards,
>>>> Ikegami
>>>>
>>>>> Cheers and thanks again,
>>>>> Ahmad
>>>>>
>>>>>> Regards,
>>>>>> Ikegami
>>>>>>
>>>>>>> Regards,
>>>>>>> Ikegami
>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> Ahmad
>>>>>>>>
>>>>>>>>
>