From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx186.postini.com [74.125.245.186]) by kanga.kvack.org (Postfix) with SMTP id 3B4A96B004D for ; Wed, 21 Dec 2011 14:02:50 -0500 (EST) Received: by werf1 with SMTP id f1so3962233wer.14 for ; Wed, 21 Dec 2011 11:02:48 -0800 (PST) Date: Wed, 21 Dec 2011 20:04:33 +0100 From: Daniel Vetter Subject: Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism Message-ID: <20111221190433.GE3827@phenom.ffwll.local> 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org