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 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
