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[209.85.166.171]) by smtp.gmail.com with ESMTPSA id e16sm548628iow.37.2020.07.14.20.46.16 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jul 2020 20:46:17 -0700 (PDT) Received: by mail-il1-f171.google.com with SMTP id o3so744589ilo.12 for ; Tue, 14 Jul 2020 20:46:16 -0700 (PDT) X-Received: by 2002:a92:a196:: with SMTP id b22mr7685147ill.303.1594784776244; Tue, 14 Jul 2020 20:46:16 -0700 (PDT) MIME-Version: 1.0 References: <20200713091211.2183368-1-tientzu@chromium.org> <20200713091211.2183368-2-tientzu@chromium.org> <4a2451f9-57d8-2e83-e1d6-f144f37173c0@arm.com> <20200714110141.GD16178@lst.de> In-Reply-To: <20200714110141.GD16178@lst.de> From: Claire Chang Date: Wed, 15 Jul 2020 11:46:05 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/4] dma-mapping: Add bounced DMA ops To: Christoph Hellwig Cc: Nicolas Boichat , devicetree@vger.kernel.org, heikki.krogerus@linux.intel.com, saravanak@google.com, suzuki.poulose@arm.com, Robin Murphy , lkml , bgolaszewski@baylibre.com, iommu@lists.linux-foundation.org, Rob Herring , Greg KH , dan.j.williams@intel.com, treding@nvidia.com, frowand.list@gmail.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Tue, Jul 14, 2020 at 7:01 PM Christoph Hellwig wrote: > > On Mon, Jul 13, 2020 at 12:55:43PM +0100, Robin Murphy wrote: > > On 2020-07-13 10:12, Claire Chang wrote: > >> The bounced DMA ops provide an implementation of DMA ops that bounce > >> streaming DMA in and out of a specially allocated region. Only the > >> operations relevant to streaming DMA are supported. > > > > I think there are too many implicit assumptions here - apparently that > > coherent allocations will always be intercepted by > > dma_*_from_dev_coherent(), and that calling into dma-direct won't actually > > bounce things a second time beyond where you thought they were going, > > manage coherency for a different address, and make it all go subtly wrong. > > Consider "swiotlb=force", for instance... > > > > Again, plumbing this straight into dma-direct so that SWIOTLB can simply > > target a different buffer and always bounce regardless of masks would seem > > a far better option. > > I haven't really had time to read through the details, but I agree that > any bouncing scheme should reuse the swiotlb code and not invent a > parallel infrastructure. Thanks for the feedback. I'll try to reuse SWIOTLB. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu