Question regarding changing video adapter selection during pre-boot (PEI/DXE)

Question regarding changing video adapter selection during pre-boot (PEI/DXE)

[pharcellus]

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Greetings, all.

I have kind of a general UEFI dev question. I have multiple video adapters in a system in which the BIOS doesn't provide even a hidden means of selecting a particular adapter to use as the default boot adapter. It seems like the heuristic is similar to what vgaarb does in the Linux kernel, where it takes the adapter with the highest available PCI device ID and that one becomes the active boot adapter.

I've read a bit of the UEFI spec about the GOP protocol, but what I wanted to know was where I could look for the code that makes the determination for the heuristic. Does it reside in a DXE driver module, or is it in a different location? If so, could you tell me which one or where might I look to find it?

Also, is there a way without patching a UEFI BIOS to change that heuristic if the BIOS itself doesn't provide a setup option? Like, could I add a DXE driver to change it, or some other driver in the boot EFI partition? (I would tend to think it would be too late at that point, but figured I would ask).

Thank you in advance for any advice,
Talarus Luan

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