Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965209AbbBBVqc (ORCPT ); Mon, 2 Feb 2015 16:46:32 -0500 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:43620 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965153AbbBBVqa (ORCPT ); Mon, 2 Feb 2015 16:46:30 -0500 Date: Mon, 2 Feb 2015 21:46:16 +0000 From: Russell King - ARM Linux To: Rob Clark Cc: Sumit Semwal , LKML , "linux-media@vger.kernel.org" , DRI mailing list , Linaro MM SIG Mailman List , "linux-arm-kernel@lists.infradead.org" , "linux-mm@kvack.org" , Linaro Kernel Mailman List , Tomasz Stanislawski , Robin Murphy , Marek Szyprowski , Daniel Vetter Subject: Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms Message-ID: <20150202214616.GI8656@n2100.arm.linux.org.uk> References: <1422347154-15258-1-git-send-email-sumit.semwal@linaro.org> <1422347154-15258-2-git-send-email-sumit.semwal@linaro.org> <20150129143908.GA26493@n2100.arm.linux.org.uk> <20150129154718.GB26493@n2100.arm.linux.org.uk> <20150129192610.GE26493@n2100.arm.linux.org.uk> <20150202165405.GX14009@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1685 Lines: 36 On Mon, Feb 02, 2015 at 03:30:21PM -0500, Rob Clark wrote: > On Mon, Feb 2, 2015 at 11:54 AM, Daniel Vetter wrote: > >> My initial thought is for dma-buf to not try to prevent something than > >> an exporter can actually do.. I think the scenario you describe could > >> be handled by two sg-lists, if the exporter was clever enough. > > > > That's already needed, each attachment has it's own sg-list. After all > > there's no array of dma_addr_t in the sg tables, so you can't use one sg > > for more than one mapping. And due to different iommu different devices > > can easily end up with different addresses. > > > Well, to be fair it may not be explicitly stated, but currently one > should assume the dma_addr_t's in the dmabuf sglist are bogus. With > gpu's that implement per-process/context page tables, I'm not really > sure that there is a sane way to actually do anything else.. That's incorrect - and goes dead against the design of scatterlists. Not only that, but it is entirely possible that you may get handed memory via dmabufs for which there are no struct page's associated with that memory - think about display systems which have their own video memory which is accessible to the GPU, but it isn't system memory. In those circumstances, you have to use the dma_addr_t's and not the pages. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/