From: Artem Bityutskiy <dedekind1@gmail.com>
To: Nikolaus Voss <n.voss@weinmann.de>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>,
linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mtd: atmel_nand: fix access to 16 bit NAND devices
Date: Fri, 27 Jan 2012 15:29:56 +0200 [thread overview]
Message-ID: <1327670996.26648.43.camel@sauron.fi.intel.com> (raw)
In-Reply-To: <201201251217.q0PCHmRe027024@gatekeeper.vosshq.de>
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On Wed, 2012-01-18 at 10:16 +0100, Nikolaus Voss wrote:
> commit fb5427508abbd635e877fabdf55795488119c2d6 optimizes PIO
> NAND accesses by using IO memcpy instead of IO read/write
> repeated functions.
>
> This breaks access to 16 bit NAND devices as memcpy_fromio()/toio()
> _always_ use byte accesses (see arch/arm/kernel/io.c), so with
> 16 bit NAND, one byte gets lost per NAND access cycle and NAND
> address count is wrong.
>
> Using memcpy() instead of the IO memcpy functions fixes this, but
> depends on correct word alignment of the buffer and length has to
> be a multiple of four, otherwise it might issue byte accesses and
> possibly break 16 bit NAND access (cf arch/arm/lib/copy_template.S).
>
> Memcpy variants seem to be the wrong approach here, since the
> NAND controller doesn't make the NAND appear as truely randomly
> accessible memory (as opposed to the DRAM controller which does
> exactly that).
>
> So, my proposal is to use 32 bit IO read/write (and let SMC
> map it to 8 bit or 16 bit NAND accesses) and account for
> length % 4 > 0 with two additional IO read/writes.
>
> Signed-off-by: Nikolaus Voss <n.voss@weinmann.de>
Why not to revert fb5427508abbd635e877fabdf55795488119c2d6 instead, it
is in my opinion a bit more readable?
--
Best Regards,
Artem Bityutskiy
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next prev parent reply other threads:[~2012-01-27 13:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-18 9:16 [PATCH] mtd: atmel_nand: fix access to 16 bit NAND devices Nikolaus Voss
2012-01-27 13:29 ` Artem Bityutskiy [this message]
2012-01-30 7:57 ` Voss, Nikolaus
2012-01-30 8:57 ` Nicolas Ferre
2012-02-01 10:43 ` Eric Bénard
2012-02-02 12:06 ` Artem Bityutskiy
2012-02-03 3:35 ` Venu Byravarasu
2012-02-03 5:32 ` Artem Bityutskiy
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