[PATCH xserver 4/4] xfree86: promote one GPU screen if (NumScreens == 0 && NumGPUScreens > 0)

Adam Jackson ajax at redhat.com
Tue Sep 6 14:52:49 UTC 2016

On Tue, 2016-09-06 at 08:32 +1000, Dave Airlie wrote:

> Primary means the card the firmware/BIOS shows up on, and I understand
> in ARM world that probably doesn't mean much as the firmware/BIOS might
> not show up on any.
> On x86 the primary GPU is the one the BIOS inits first, not the onboard,
> you can usually pick in the BIOS what the GPU boot order is, and Linux uses
> whatever is the VGA card as the primary to respect that.
> So on aarch64/arm we could have the kernel pick one GPU is there is only
> one and mark it as primary. I'm not sure if this would need device tree support
> or not etc.
> In the absence of policy from the kernel, I'd rather not put the policy in the X
> server code itself. As boot probe ordering could mean we'd pick different
> primaries on different boots if things raced which doesn't seem ideal.

This would only be true if there are multiple devices. A policy of "if
there's no kernel primary but only one device, treat that one as the
primary" seems infinitely better than not having it, in which case the
policy is effectively "well you only have one video card but I don't
know which one you want me to use".

- ajax

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