From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754177Ab1LUTCw (ORCPT ); Wed, 21 Dec 2011 14:02:52 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:51555 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753009Ab1LUTCt (ORCPT ); Wed, 21 Dec 2011 14:02:49 -0500 Date: Wed, 21 Dec 2011 20:04:33 +0100 From: Daniel Vetter To: Arnd Bergmann Cc: Daniel Vetter , linux@arm.linux.org.uk, "Semwal, Sumit" , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, Rob Clark , linux-arm-kernel@lists.infradead.org, Alan Cox , linux-media@vger.kernel.org Subject: Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism Message-ID: <20111221190433.GE3827@phenom.ffwll.local> Mail-Followup-To: Arnd Bergmann , linux@arm.linux.org.uk, "Semwal, Sumit" , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, Rob Clark , linux-arm-kernel@lists.infradead.org, Alan Cox , linux-media@vger.kernel.org References: <1322816252-19955-1-git-send-email-sumit.semwal@ti.com> <20111220171437.GC3883@phenom.ffwll.local> <201112211727.17104.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201112211727.17104.arnd@arndb.de> X-Operating-System: Linux phenom 3.1.0-1-amd64 User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 21, 2011 at 05:27:16PM +0000, Arnd Bergmann wrote: > On Tuesday 20 December 2011, Daniel Vetter wrote: > > It also sounds like that at least for proper userspace mmap support we'd > > need some dma api extensions on at least arm, and that might take a while > > ... > > I think it's actually the opposite -- you'd need dma api extensions on > everything else other than arm, which already has dma_mmap_coherent() > and dma_mmap_writecombine() for this purpose. Yeah, that's actually what I wanted to say, but failed at ... Another thing is that at least for i915, _writecombine isn't what we want actually because: - It won't work anyway cause i915 maps stuff cached and does the flushing itself and x86 PAT doesn't support mixed mappings (kinda like arm). - It isn't actually enough, there's another hidden buffer between the memory controller interface and the gpu that i915 manually flushes (because even a readback on a wc mapping doesn't flush things in there). So I assume we'll have plenty of funny beating out a good api for cpu access ;-) Cheers, Daniel -- Daniel Vetter Mail: daniel@ffwll.ch Mobile: +41 (0)79 365 57 48