From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757095AbZHGHqV (ORCPT ); Fri, 7 Aug 2009 03:46:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755609AbZHGHqU (ORCPT ); Fri, 7 Aug 2009 03:46:20 -0400 Received: from perceval.irobotique.be ([92.243.18.41]:59747 "EHLO perceval.irobotique.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755168AbZHGHqU (ORCPT ); Fri, 7 Aug 2009 03:46:20 -0400 From: Laurent Pinchart To: "Russell King - ARM Linux" Subject: Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?") Date: Fri, 7 Aug 2009 09:48:24 +0200 User-Agent: KMail/1.11.4 (Linux/2.6.30.3; KDE/4.2.4; x86_64; ; ) Cc: David Xiao , Ben Dooks , Hugh Dickins , Robin Holt , "linux-kernel@vger.kernel.org" , "v4l2_linux" , "linux-arm-kernel@lists.arm.linux.org.uk" References: <200908061208.22131.laurent.pinchart@ideasonboard.com> <1249584374.29182.20.camel@david-laptop> <20090806222543.GG31579@n2100.arm.linux.org.uk> In-Reply-To: <20090806222543.GG31579@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200908070948.26389.laurent.pinchart@ideasonboard.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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