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

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Message-ID: <cedb1604-e024-2738-5b33-15703a653803@gmail.com>
Date:   Tue, 15 Feb 2022 03:46:18 +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 Ahmad-san,

On 2022/02/15 1:22, Ahmad Fatoum wrote:
> Hello Tokunori-san,
>
> On 13.02.22 17:47, Tokunori Ikegami wrote:
>> Hi Ahmad-san,
>>
>> Thanks for your confirmations. Sorry for late to reply.
> No worries. I appreciate you taking the time.
>
>> Could you please try the patch attached to disable the chip_good() change as before?
>> I think this should work for S29GL964N since the chip_ready() is used and works as mentioned.
> yes, this resolves my issue:
> Tested-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
Thanks for your testing. I have just sent the patch to review.
>
>>>>> Doesn't seem to be a buffered write issue here though as the writes
>>>>> did work fine before dfeae1073583. Any other ideas?
>>>> At first I thought the issue is possible to be resolved by using the word write instead of the buffered writes.
>>>> Now I am thinking to disable the changes dfeae1073583 partially with any condition if possible.
>>> 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.

Regards,
Ikegami

>
> Cheers,
> Ahmad
>
>