linux-kernel - Re: [PATCH] mtd: spi-nor: fix DMA unsafe buffer issue in spi_nor_read

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Message-ID: <CAMuHMdVGnrwgcoXuRSy+A7O5+_fKQyH1XHGKrm0WSWAEw3SorA@mail.gmail.com>
Date:   Thu, 7 Sep 2017 13:44:22 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Marek Vasut <marek.vasut@...il.com>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Richard Weinberger <richard@....at>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] mtd: spi-nor: fix DMA unsafe buffer issue in spi_nor_read_sfdp()

Hi Boris,

On Thu, Sep 7, 2017 at 1:37 PM, Boris Brezillon
<boris.brezillon@...e-electrons.com> wrote:
> On Thu, 7 Sep 2017 10:00:50 +0200
> Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> Instead of having buffers on the stack, passing them around through multiple
>> call levels, and then kmalloc()ing a buffer, what about using the helpers in
>> <linux/spi/spi.h> instead, which take care of the issue through the
>> static bounce
>> buffer or kmalloc() themselves?
>
> Are you referring to spi_write_then_read()? If this is the case, I'm not

For example. There are more of them.

> sure we can use this because m25p80_read/write() can have more than 2
> transfers.

OK.More than two transfers may need special handling.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds