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Date: Fri, 7 Aug 2009 10:12:23 +0200
From: Matthieu CASTET <matthieu.castet@parrot.com>
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To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
CC: David Xiao <dxiao@broadcom.com>, Ben Dooks <ben-linux@fluff.org>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>, Robin Holt <holt@sgi.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       v4l2_linux <linux-media@vger.kernel.org>,
       "linux-arm-kernel@lists.arm.linux.org.uk" 
	<linux-arm-kernel@lists.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 ?")
References: <200908061208.22131.laurent.pinchart@ideasonboard.com>	<200908061506.23874.laurent.pinchart@ideasonboard.com>	<1249584374.29182.20.camel@david-laptop> <200908070929.53873.laurent.pinchart@ideasonboard.com>
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Laurent Pinchart a écrit :
> On Thursday 06 August 2009 20:46:14 David Xiao wrote:
> 
> Think about the simple following use case. An application wants to display 
> video it acquires from the device to the screen using Xv. The video buffer is 
> allocated by Xv. Using the v4l2 user pointer streaming method, the device can 
> DMA directly to the Xv buffer. Using driver-allocated buffers, a memcpy() is 
> required between the v4l2 buffer and the Xv buffer.
> 
v4l2 got an API (overlay IRRC) that allow drivers to write directly in
framebuffer memory.
BTW Xv buffer is not always in video memory and the X driver can do a
memcpy.


Matthieu