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

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Date:   Fri, 4 Mar 2022 12:11:32 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Tokunori Ikegami <ikegami.t@...il.com>,
        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

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.

> 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.

>>>>> 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.

Cheers and thanks again,
Ahmad

> 
> Regards,
> Ikegami
> 
>>
>> Regards,
>> Ikegami
>>
>>>
>>> Cheers,
>>> Ahmad
>>>
>>>


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