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

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Date:   Fri, 13 Oct 2017 17:34:30 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Mason <slash.tmp@...e.fr>, Richard Weinberger <richard@....at>,
        LKML <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2 0/2] mtd: nand: wait for tWHR, and fix the
 setup_data_interface of Denali

Hi Marc,

2017-10-04 20:05 GMT+09:00 Marc Gonzalez <marc_gonzalez@...madesigns.com>:
> 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?

It is odd to use dev_ready() hook to insert delay for the READ ID command.
READ ID command never toggles the device's Ready/Busy# pin.


> When I have more time, I will test the 4.14
> branch, to see if there are any issues with the current driver.


Yeah, I highly recommend you to test your driver on the latest kernel.
I suspect it is broken because READ ID command in the generic hook
has absolutely zero delay.

As I proposed already, the correct fix it to wait for tWHR.




-- 
Best Regards
Masahiro Yamada