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SubjectRe: [PATCH] radeon: Test for PCI root bus before assuming bus->self
On Wed, Aug 27, 2014 at 9:32 PM, Dave Airlie <> wrote:
>> On Wed, Aug 27, 2014 at 3:01 PM, Alex Williamson
>> <> 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 <>
> Does this mean inside a VM we can't enable pcie 2 speeds?
> This could lead to a quite disappointing speed decrease for DMA transfers.

It depends on the sbios, but most boards negotiate the highest speed at boot.


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