From: "Voss, Nikolaus" <N.Voss@weinmann.de>
To: "'dedekind1@gmail.com'" <dedekind1@gmail.com>
Cc: "'Nicolas Ferre'" <nicolas.ferre@atmel.com>,
"'linux-mtd@lists.infradead.org'" <linux-mtd@lists.infradead.org>,
"'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] mtd: atmel_nand: fix access to 16 bit NAND devices
Date: Mon, 30 Jan 2012 08:57:17 +0100 [thread overview]
Message-ID: <EF2E73589CA71846A15D0B2CDF79505D08AD3E5453@wm021.weinmann.com> (raw)
In-Reply-To: <1327670996.26648.43.camel@sauron.fi.intel.com>
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Artem Bityutskiy wrote on 2012-01-27:
> 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?
No objections. I've tried to save the idea of
fb5427508abbd635e877fabdf55795488119c2d6 but that length % 4 > 0 stuff
uglifies it a little bit...
Niko
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next prev parent reply other threads:[~2012-01-30 8:14 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
2012-01-30 7:57 ` Voss, Nikolaus [this message]
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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