linux-kernel - Re: dma_unmap_single() lacking cache sync on some archs?

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Date:	Tue, 27 Sep 2011 14:13:34 +0200
From:	Arvid Brodin <arvid.brodin@...a.com>
To:	<linux-kernel@...r.kernel.org>
CC:	<linux-embedded@...r.kernel.org>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	Haavard Skinnemoen <hskinnemoen@...il.com>, <arnd@...db.de>
Subject: Re: dma_unmap_single() lacking cache sync on some archs?

[Resending with CC to affected parties]

Hi,

I would expect cache synchronization for DMA_TO_DEVICE and DMA_BIDIRECTIONAL
when dma_map_single() is called, and for DMA_FROM_DEVICE and DMA_BIDIRECTIONAL
when dma_unmap_single() is called.

However, on some architechtures (at least avr32, blackfin, ...), cache
synchronization only happens when dma_map_single() is called (and then
irrespective of DMA direction). dma_unmap_single() is a no-op for these archs.

See e.g. http://lxr.linux.no/#linux+v3.0.4/arch/avr32/include/asm/dma-mapping.h#L117

Isn't this a bug?

(Please CC me in responses.)

-- 
Arvid Brodin
Enea Services Stockholm AB

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