[Bug 117131] vga_switcheroo does not switch IGP -> DIS ( IGP == i915 , DIS == radeon )

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=117131

--- Comment #24 from Alex Deucher <alexdeucher at gmail.com> ---

(In reply to Jason Vas Dias from comment #20)
> When I look at linux 4.5.0 boot dmesg log messages like :
> 
> [    3.115380] vga_switcheroo: enabled
> [    3.115463] ATPX version 1, functions 0x00000033
> [    3.115541] [drm] DMAR active, disabling use of stolen memory
> 
> 
> I think 'you lie, Linux' !

The driver reads the supported ATPX functions from ACPI.  So it's a bios bug.

> 
> vga_switcheroo can never be enabled on this platform because 
> it has no MUX , and the logs above show the quality of the 
> ACPI ATPX support.
>

vga_switcheroo and ATPX are used on muxed and mux-less platforms to powerdown
the dGPU dynamically when it's not in use.

The ATPX error messages are harmless though as they are not checked anywhere.

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