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Date: Tue, 7 Jul 2009 21:43:37 +0800
Message-ID: <d82e647a0907070643i198b9188q80203ab0408b4df8@mail.gmail.com>
Subject: Re: [PATCH][RFC] asm-generic:remove calling flush_write_buffers() in 
	dma_sync_*_for_cpu
From: Ming Lei <tom.leiming@gmail.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Joerg Roedel <joerg.roedel@amd.com>, fujita.tomonori@lab.ntt.co.jp,
       linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
       linux-arm-kernel <linux-arm-kernel@lists.arm.linux.org.uk>
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2009/7/7 Russell King - ARM Linux <linux@arm.linux.org.uk>:
> On Tue, Jul 07, 2009 at 09:54:20AM +0800, Ming Lei wrote:
>> 2009/6/30 Arnd Bergmann <arnd@arndb.de>:
>> > On Tuesday 30 June 2009, Alan Cox wrote:
>> > Well, not even that. dma-mapping-common.h only makes sense on architectures
>> > that have multiple dma-mapping implementations (parisc, mips, arm, powerpc,
>>
>> It seems that there is only one dma-mmaping implementation on ARM, doesn't it?
>> Is it necessary that using dma-mapping-common.h on ARM?
>
> ARM has two (normal, and dma bounce), and in the long run we need to do

OK, Can we use dma-mapping-common.h on ARM?

> cache handling on unmap as well as map due to CPU speculative fetches.

IMHO, it seems we can fix this problem now.

For DMA_TO_DEVICE transfer, clean cache in dma map, but does nothing in
dma unmap;

For  DMA_FROM_DEVICE, we may do nothing in dma map, but invaliate cache
in dma unmap.

Is it doable?

Thanks.
-- 
Lei Ming
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