linux-kernel - Re: [PATCH][RFC] asm-generic:remove calling flush_write_buffers() in dma_sync_*_for

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Message-ID: <20090629173121.768f2923@lxorguk.ukuu.org.uk>
Date:	Mon, 29 Jun 2009 17:31:21 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Joerg Roedel <joerg.roedel@....com>, tom.leiming@...il.com,
	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH][RFC] asm-generic:remove calling flush_write_buffers()
 in dma_sync_*_for_cpu

> Wouldn't it be better to put the flush_write_buffer in the specific
> operation (swiotlb_sync_*_for_*) rather than the multiplexer?
> 
> Maybe in that case, smp_wmb() would be more appropriate because
> it is defined on all architectures.

smp_wmb() is stronger and it would slow down x86 if we did that (we'd go
from no-op on a coherent platform to using mfence/lfence etc)

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