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

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Date:   Fri, 29 Sep 2017 23:33:28 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Linux Kernel Mailing List <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>,
        Marc Gonzalez <marc_gonzalez@...madesigns.com>
Subject: Re: [PATCH v2 0/2] mtd: nand: wait for tWHR, and fix the
 setup_data_interface of Denali

(+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




commit 6ea40a3ba93e1b14ffb349e276f9dfefc4334b99
Author: Boris Brezillon <boris.brezillon@...e-electrons.com>
Date:   Sat Oct 1 10:24:03 2016 +0200

    mtd: nand: Wait tCCS after a column change

    Drivers implementing ->cmd_ctrl() and relying on the default ->cmdfunc()
    implementation usually don't wait tCCS when a column change (RNDIN or
    RNDOUT) is requested.
    Add an option flag to ask the core to do so (note that we keep this as
    an opt-in to avoid breaking existing implementations), and make use of
    the ->data_interface information is available (otherwise, wait 500ns).

    Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
    Tested-by: Marc Gonzalez <marc_gonzalez@...madesigns.com>


-- 
Best Regards
Masahiro Yamada