linux-kernel - Re: [PATCH v2 0/2] mtd: nand: wait for tWHR, and fix the setup_data

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Date:   Wed, 4 Oct 2017 13:05:11 +0200
From:   Marc Gonzalez <marc_gonzalez@...madesigns.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:     linux-mtd <linux-mtd@...ts.infradead.org>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        LKML <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH v2 0/2] mtd: nand: wait for tWHR, and fix the
 setup_data_interface of Denali

On 29/09/2017 16:33, Masahiro Yamada wrote:

> (+CC Marc Gonzalez)
> 
> 2017-09-29 21:26 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
>> On Fri, 29 Sep 2017 19:38:38 +0900
>> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>>
>>> 1/2 : add NAND_WAIT_TWHR and nand_whr_delay().
>>>       You can set this new flag if you want nand_command(_lp)
>>>       to insert tWHR delay where needed.
>>>
>>> 2/2 : Fix Denali setup_data_interface.
>>>       Boris' suggestion in v1 was a good reminder that
>>>       made me realize tCCS was missing in the driver.  Fix it now.
>>>
>>>
>>> Changes in v2:
>>>   - Add nand_whr_delay() helper
>>>     Wait for tWHR only for drivers that explicitly set NAND_WAIT_TWHR flag
>>>   - newly added
>>>
>>> Masahiro Yamada (2):
>>>   mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID
>>
>> Hm, I thought you were introducing this to then use it in the denali
>> driver. Sorry, but I don't want to apply something that nobody needs.
>> If someone ever complains about a missing delay I'll point him to your
>> patch, but until then I'll keep the core unchanged.
> 
> Perhaps, Marc Gonzalez is the person.
> 
> 
> tango_nand.c is the only driver that sets NAND_WAIT_TCCS.
> 
> Now, there is completely no delay when reading out the ID.
> 
> 
> One safe change might be apply this patch,
> then set NAND_WAIT_TWHR to tango_nand.c
> 
> 
> I am guessing NAND_WAIT_TCCS was added for it.
> Theoretically, I do not see logical difference between tCCS and tWHR.
> 
> I am CCing Marc Gonzalez, the author of tango_nand.c

Hello Masahiro,

I remember having issues reading the ONFI ID when I was writing
the driver, a year ago. Sometimes, the first few bytes appeared
to be missing. This looked like a timing issue.

Adding the dev_ready call-back solved the problem. Do you think
that was by accident? When I have more time, I will test the 4.14
branch, to see if there are any issues with the current driver.

Regards.