linux-kernel - Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?")

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Message-Id: <200908070948.26389.laurent.pinchart@ideasonboard.com>
Date:	Fri, 7 Aug 2009 09:48:24 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	"Russell King - ARM Linux" <linux@....linux.org.uk>
Cc:	David Xiao <dxiao@...adcom.com>, Ben Dooks <ben-linux@...ff.org>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Robin Holt <holt@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"v4l2_linux" <linux-media@...r.kernel.org>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>
Subject: Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?")

On Friday 07 August 2009 00:25:43 Russell King - ARM Linux wrote:
>
> As far as userspace DMA coherency, the only way you could do it with
> current kernel APIs is by using get_user_pages(), creating a scatterlist
> from those, and then passing it to dma_map_sg().  While the device has
> ownership of the SG, userspace must _not_ touch the buffer until after
> DMA has completed.

If the buffers are going to be reused again and again, would it be possible to 
mark the pages returned by get_user_pages() as non-cacheable instead ?

Regards,

Laurent Pinchart

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