On Fri, Jun 12, 2020 at 11:47:55AM +0200, Thomas Zimmermann wrote: > Hi > > Am 12.06.20 um 03:36 schrieb Gurchetan Singh: > > This is useful for the next patch. Also, should we only unmap the > > amount entries that we mapped with the dma-api? > > It looks like you're moving virtio code into shmem. Well, not really. virtio has -- for historical reasons -- the oddity that it may or may not need to dma_map resources, depending on device configuration. Initially virtio went with "it's just a vm, lets simply operate on physical ram addresses". That shortcut turned out to be a bad idea later on, especially with the arrival of iommu emulation support in qemu. But we couldn't just scratch it for backward compatibility reasons. See virtio_has_iommu_quirk(). This just allows to enable/disable dma_map, I guess to fix some fallout from recent shmem helper changes (Gurchetan, that kind of stuff should be mentioned in cover letter and commit messages). I'm not sure virtio actually needs that patch though. I *think* doing the dma_map+dma_unmap unconditionally, but then ignore the result in case we don't need it should work. And it shouldn't be a horrible performance hit either, in case we don't have a (virtual) iommu in the VM dma mapping is essentially a nop ... take care, Gerd _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
