linux-kernel - Re: [PATCH v6 00/18] mtd: nand: denali: Denali NAND IP patch bomb

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Date:   Tue, 13 Jun 2017 17:52:55 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Dinh Nguyen <dinguyen@...nel.org>,
        Enrico Jorns <ejo@...gutronix.de>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Chuanxiao Dong <chuanxiao.dong@...el.com>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v6 00/18] mtd: nand: denali: Denali NAND IP patch bomb

Hi Boris,

2017-06-13 17:30 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> On Tue, 13 Jun 2017 17:17:41 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>
>> Hi Boris,
>>
>>
>> 2017-06-13 16:02 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
>>
>> >
>> > BTW, I also implemented ->read/write_buf_word() since the core may one
>> > day call these functions, and the default implementations used by the
>> > core when these hooks are NULL are not appropriate in your case.
>> >
>>
>> BTW, why doesn't the default hook in the core do like this?
>>
>>
>> static uint8_t nand_read_byte(struct mtd_info *mtd)
>> {
>>         struct nand_chip *chip = mtd_to_nand(mtd);
>>         uint8_t byte;
>>
>>         chip->read_buf(chip, &byte, 1);
>>         return byte;
>> }
>>
>>
>> ->read_byte() is a special case of ->read_buf() with length==1,
>> so this should work.
>
> Not sure it works for all implementation. ->read_byte() is expected
> to return the lower 8 bits when interacting with a 16-bits bus. If we do
> what you suggest, and ->read_buf() appears to be caching data in an
> intermediate buffer if the amount of data is not aligned on 2 bytes,
> you might retrieve data you don't care about when ->read_byte() is
> called several times.

You are right.

I missed the case where ->read_byte() is called repeatedly.

Thanks!



-- 
Best Regards
Masahiro Yamada