Re: [PATCH] PCI/VGA: Look at all PCI display devices in VGA arbiter

[Lukas Wunner <lukas@wunner.de>]

On Fri, Jun 13, 2025 at 04:47:20PM -0500, Daniel Dadap wrote:
> Ideally we'd be able to actually query which GPU is connected to the panel
> at the time we're making this determination, but I don't think there's a
> uniform way to do this at the moment. Selecting the integrated GPU seems
> like a reasonable heuristic, since I'm not aware of any systems where the
> internal panel defaults to dGPU connection, since that would defeat the
> purpose of having a hybrid GPU system in the first place

Intel-based dual-GPU MacBook Pros boot with the panel switched to the
dGPU by default.  This is done for Windows compatibility because Apple
never bothered to implement dynamic GPU switching on Windows.

The boot firmware can be told to switch the panel to the iGPU via an
EFI variable, but that's not something the kernel can or should depend on.

MacBook Pros introduced since 2013/2014 hide the iGPU if the panel is
switched to the dGPU on boot, but the kernel is now unhiding it since
71e49eccdca6.

I don't pretend to fully understand the consequences of the proposed
patch, just want to highlight the regression potential on Apple machines
and probably others.

Thanks,

Lukas