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[109.64.41.91]) by smtp.gmail.com with ESMTPSA id h29sm24085wrc.78.2020.06.08.08.17.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jun 2020 08:17:21 -0700 (PDT) Date: Mon, 8 Jun 2020 11:17:18 -0400 From: "Michael S. Tsirkin" To: David Stevens Cc: Gerd Hoffmann , David Airlie , Daniel Vetter , Jason Wang , Sumit Semwal , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , open list , ML dri-devel , "open list:VIRTIO GPU DRIVER" , Linux Media Mailing List , "moderated list:DMA BUFFER SHARING FRAMEWORK" , virtio-dev@lists.oasis-open.org Subject: Re: [PATCH v3 4/4] drm/virtio: Support virtgpu exported resources Message-ID: <20200608111647-mutt-send-email-mst@kernel.org> References: <20200311112004.47138-1-stevensd@chromium.org> <20200311112004.47138-5-stevensd@chromium.org> <20200513123326-mutt-send-email-mst@kernel.org> <20200608054234-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Mon, Jun 08, 2020 at 07:36:55PM +0900, David Stevens wrote: > On Mon, Jun 8, 2020 at 6:43 PM Michael S. Tsirkin wrote: > > > > On Fri, May 15, 2020 at 04:26:15PM +0900, David Stevens wrote: > > > > > + if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_RESOURCE_UUID)) { > > > > > + vgdev->has_resource_assign_uuid = true; > > > > > + } > > > > > > > > > > > > Just a question: this relies on DMA bufs so I assume it is > > > > not really assumed to work when DMA API is bypassed, right? > > > > Rather than worry what does it mean, how about just > > > > disabling this feature without PLATFORM_DMA for now? > > > > > > By PLATFORM_DMA, do you mean CONFIG_DMA_SHARED_BUFFER? > > > > Sorry, no. I mean VIRTIO_F_IOMMU_PLATFORM which in the > > future will be renamed to VIRTIO_F_PLATFORM_ACCESS. > > Shouldn't things work independent of whether or not that feature is > set? If a virtio driver properly uses the dma_buf APIs (which virtgpu > seems to), then that should take care of any mapping/synchronization > related to VIRTIO_F_IOMMU_PLATFORM. If anything, the case where > VIRTIO_F_IOMMU_PLATFORM isn't set is easier, since then we know that > the "the device has same access [sic] to memory addresses supplied to > it as the driver has", according to the specification. > > -David I don't know much about drm so I can't tell, I was hoping Gerd can explain. -- MST