On Thu, 2014-08-28 at 11:32 +1000, Dave Airlie wrote: > > On Wed, Aug 27, 2014 at 3:01 PM, Alex Williamson > > <alex.williamson@xxxxxxxxxx> wrote: > >> If we assign a Radeon device to a virtual machine, we can no longer > >> assume a fixed hardware topology, like the GPU having a parent device. > >> This patch simply adds a few pci_is_root_bus() tests to avoid passing > >> a NULL pointer to PCI access functions, allowing the radeon driver to > >> work in a QEMU 440FX machine with an assigned HD8570 on the emulated > >> PCI root bus. > >> > >> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > > Does this mean inside a VM we can't enable pcie 2 speeds? Shouldn't the device already be set to something reasonable before it's assigned? > This could lead to a quite disappointing speed decrease for DMA transfers. We couldn't do it before anyway, there's no decrease. Even with a Q35 QEMU chipset the best we were doing was tweaking dummy registers on the upstream port. Should VFIO be doing bus tuning prior to exposing the device? I suppose our other option would be to let the link control bits of the emulated downstream port pass through to the host. In any case, I don't see that this patch limits performance any more than it already is for a VM. Thanks, Alex _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
