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Thu, 15 Oct 2020 08:33:36 -0700 (PDT) Date: Thu, 15 Oct 2020 17:33:34 +0200 From: Daniel Vetter To: Christoph Hellwig Subject: Re: [PATCH 2/3] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for non-coherent cache maintenance Message-ID: <20201015153334.GF438822@phenom.ffwll.local> Mail-Followup-To: Christoph Hellwig , Robin Murphy , Jonathan Marek , David Airlie , freedreno@lists.freedesktop.org, open list , "open list:DRM DRIVER FOR MSM ADRENO GPU" , iommu@lists.linux-foundation.org, "open list:DRM DRIVER FOR MSM ADRENO GPU" , Sean Paul References: <20201001002709.21361-3-jonathan@marek.ca> <20201002075321.GA7547@infradead.org> <20201005082914.GA31702@infradead.org> <3e0b91be-e4a4-4ea5-7d58-6e71b8d51932@marek.ca> <20201006072306.GA12834@infradead.org> <148a1660-f0fc-7163-2240-6b94725342b5@marek.ca> <20201007062519.GA23519@infradead.org> <20201015065532.GA15371@infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201015065532.GA15371@infradead.org> X-Operating-System: Linux phenom 5.7.0-1-amd64 Cc: Sean Paul , Jonathan Marek , David Airlie , Robin Murphy , open list , "open list:DRM DRIVER FOR MSM ADRENO GPU" , iommu@lists.linux-foundation.org, Daniel Vetter , "open list:DRM DRIVER FOR MSM ADRENO GPU" , freedreno@lists.freedesktop.org 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 Thu, Oct 15, 2020 at 07:55:32AM +0100, Christoph Hellwig wrote: > On Tue, Oct 13, 2020 at 02:42:38PM +0100, Robin Murphy wrote: > > I still think this situation would be best handled with a variant of > > dma_ops_bypass that also guarantees to bypass SWIOTLB, and can be set > > automatically when attaching to an unmanaged IOMMU domain. > > dma_ops_bypass should mostly do the right thing as-is. swiotlb bouncing > is triggered of two things: > > 1) the dma_mask. This is under control of the driver, and obviously > if it is too small for a legit reason we can't just proceed Somewhat related, but is there a way to tell the dma-api to fail instead of falling back to swiotlb? In many case for gpu drivers it's much better if we fall back to dma_alloc_coherent and manage the copying ourselves instead of abstracting this away in the dma-api. Currently that's "solved" rather pessimistically by always allocating from dma_alloc_coherent if swiotlb could be in the picture (at least for ttm based drivers, i915 just falls over). -Daniel > 2) force_dma_unencrypted() - we'd need to do an opt-out here, either > by a flag or by being smart and looking for an attached iommu on > the device > > > That way the > > device driver can make DMA API calls in the appropriate places that do the > > right thing either way, and only needs logic to decide whether to use the > > returned DMA addresses directly or ignore them if it knows they're > > overridden by its own IOMMU mapping. > > I'd be happy to review patches for this. -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu