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: <4A7BE1E7.60203@parrot.com>
Date:	Fri, 7 Aug 2009 10:12:23 +0200
From:	Matthieu CASTET <matthieu.castet@...rot.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
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 ?")

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
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