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

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Date:   Mon, 7 Mar 2022 00:49:39 +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 2022/03/04 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?
>
>> 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.

Regards,
Ikegami

>
> Cheers and thanks again,
> Ahmad
>
>> Regards,
>> Ikegami
>>
>>> Regards,
>>> Ikegami
>>>
>>>> Cheers,
>>>> Ahmad
>>>>
>>>>
>
View attachment "v2-0001-mtd-cfi_cmdset_0002-Use-chip_ready-for-write-on-S.patch" of type "text/x-patch" (6844 bytes)