linux-kernel - Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD

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Message-ID: <CAK7LNASpP9qQABLqXPqz8bQNsMjuxb8GKHU4Xxy_dAhgzT2O2A@mail.gmail.com>
Date:   Tue, 26 Sep 2017 17:17:49 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Richard Weinberger <richard@....at>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID

2017-09-26 15:43 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> On Tue, 26 Sep 2017 12:39:24 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>
>> Read Status and Read ID require tWHR before reading the first data.
>> Insert a very short wait to make sure to meet the spec.
>>
>> I have not seen any problem report for now, but nand_command() and
>> nand_command_lP() are generic hooks, so it makes sense to implement
>> fail-safe code here.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> ---
>


OK, will do.



BTW, I see unconditional wait for tWB a few lines below,
but it gives no performance regression because we will wait
much longer in nand_wait_ready().


     /*
      * Apply this short delay always to ensure that we do wait tWB in
      * any case on any machine.
      */
     ndelay(100);

     nand_wait_ready(mtd);




-- 
Best Regards
Masahiro Yamada