linux-kernel - Re: [Linaro-mm-sig] [PATCHv2 3/6] common: dma-mapping: introduce dma_get

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Message-ID: <20120613185251.GN4829@phenom.ffwll.local>
Date:	Wed, 13 Jun 2012 20:52:51 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Abhinav Kochhar <abhinav.k@...sung.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Subash Patel <subash.ramaswamy@...aro.org>
Subject: Re: [Linaro-mm-sig] [PATCHv2 3/6] common: dma-mapping: introduce
 dma_get_sgtable() function

On Wed, Jun 13, 2012 at 01:50:15PM +0200, Marek Szyprowski wrote:
> This patch adds dma_get_sgtable() function which is required to let
> drivers to share the buffers allocated by DMA-mapping subsystem. Right
> now the driver gets a dma address of the allocated buffer and the kernel
> virtual mapping for it. If it wants to share it with other device (= map
> into its dma address space) it usually hacks around kernel virtual
> addresses to get pointers to pages or assumes that both devices share
> the DMA address space. Both solutions are just hacks for the special
> cases, which should be avoided in the final version of buffer sharing.
> 
> To solve this issue in a generic way, a new call to DMA mapping has been
> introduced - dma_get_sgtable(). It allocates a scatter-list which
> describes the allocated buffer and lets the driver(s) to use it with
> other device(s) by calling dma_map_sg() on it.
> 
> This patch provides a generic implementation based on virt_to_page()
> call. Architectures which require more sophisticated translation might
> provide their own get_sgtable() methods.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Reviewed-by: Kyungmin Park <kyungmin.park@...sung.com>

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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