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Date:   Fri, 13 Oct 2017 17:34:30 +0900
From:   Masahiro Yamada <>
To:     Marc Gonzalez <>
Cc:     Boris Brezillon <>,
        Mason <>, Richard Weinberger <>,
        LKML <>,
        Marek Vasut <>,
        linux-mtd <>,
        Cyrille Pitchen <>,
        Brian Norris <>,
        David Woodhouse <>
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 <>:
> On 29/09/2017 16:33, Masahiro Yamada wrote:
>> (+CC Marc Gonzalez)
>> 2017-09-29 21:26 GMT+09:00 Boris Brezillon <>:
>>> On Fri, 29 Sep 2017 19:38:38 +0900
>>> Masahiro Yamada <> 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

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