[PATCH weston 2/2] compositor-drm: prefer primary GPU over other GPUs

[Dave Airlie]

On Sat, Oct 27, 2012 at 10:54 PM, David Herrmann
<dh.herrmann at googlemail.com> wrote:
> This rewrites the GPU detection of the DRM backend and uses the new PCI
> helpers to find the primary GPU. If no primary GPU is found, the first GPU
> on the seat is used.

In X I've found we only do that for seat 0, for other seats we just
use the gpu assigned to the seat.

>
> This is useful for systems with multiple GPUs that share
> display-controllers. We want to use the boot/primary GPU instead of
> possible offload-GPUs.
> Note that the kernel does not provide this information, yet, so we need to
> retrieve it via the PCI bus. It is also unclear whether the kernel will
> ever report this data as this is hardly possible to detect properly in the
> kernel.

That's how the kernel provides is via sysfs pci support, the concept
of primary GPU only makes sense for PCI devices where you have VGA
routing bits to pick the current VGA device.

Dave.