From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: MIME-Version: 1.0 In-Reply-To: <20171020145752.GA4694@lst.de> References: <1507761269-7017-6-git-send-email-jim2101024@gmail.com> <589c04cb-061b-a453-3188-79324a02388e@arm.com> <20171017081422.GA19475@lst.de> <20171018065316.GA11183@lst.de> <20171019091644.GA14983@lst.de> <20171020073730.GA12937@lst.de> <20171020145752.GA4694@lst.de> From: Jim Quinlan Date: Fri, 20 Oct 2017 11:27:41 -0400 Message-ID: Subject: Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound traffic To: Christoph Hellwig List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Linux-MIPS , Florian Fainelli , devicetree@vger.kernel.org, linux-pci , Kevin Cernekee , Will Deacon , linux-kernel@vger.kernel.org, Ralf Baechle , iommu@lists.linux-foundation.org, Rob Herring , bcm-kernel-feedback-list , Gregory Fong , Catalin Marinas , Bjorn Helgaas , Brian Norris , Robin Murphy , linux-arm-kernel@lists.infradead.org, Marek Szyprowski Content-Type: text/plain; charset="us-ascii" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+bjorn=helgaas.com@lists.infradead.org List-ID: On Fri, Oct 20, 2017 at 10:57 AM, Christoph Hellwig wrote: > On Fri, Oct 20, 2017 at 10:41:56AM -0400, Jim Quinlan wrote: >> I am not sure I understand your comment -- the size of the request >> shouldn't be a factor. Let's look at your example of the DMA request >> of 3fffff00 to 4000000f (physical memory). Lets say it is for 15 >> pages. If we block out the last page [0x3ffff000..0x3fffffff] from >> what is available, there is no 15 page span that can happen across the >> 0x40000000 boundary. For SG, there can be no merge that connects a >> page from one region to another region. Can you give an example of >> the scenario you are thinking of? > > What prevents a merge from say the regions of > 0....3fffffff and 40000000....7fffffff? Huh? [0x3ffff000...x3ffffff] is not available to be used. Drawing from the original example, we now have to tell Linux that these are now our effective memory regions: memc0-a@[ 0....3fffefff] <=> pci@[ 0....3fffefff] memc0-b@[100000000...13fffefff] <=> pci@[ 40000000....7fffefff] memc1-a@[ 40000000....7fffefff] <=> pci@[ 80000000....bfffefff] memc1-b@[300000000...33fffefff] <=> pci@[ c0000000....ffffefff] memc2-a@[ 80000000....bfffefff] <=> pci@[100000000...13fffefff] memc2-b@[c00000000...c3fffffff] <=> pci@[140000000...17fffffff] This leaves a one-page gap between phsyical memory regions which would normally be contiguous. One cannot have a dma alloc that spans any two regions. This is a drastic step, but I don't see an alternative. Perhaps I may be missing what you are saying... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel