On Wed, Mar 08, 2017 at 06:01:54AM +0100, Lukas Wunner wrote: > On Tue, Mar 07, 2017 at 03:30:30PM -0500, Alex Deucher wrote: > > On Fri, Feb 24, 2017 at 2:19 PM, Lukas Wunner <lukas at wunner.de> wrote: > > > An external Thunderbolt GPU can neither drive the laptop's panel nor be > > > powered off by the platform, so there's no point in registering it with > > > vga_switcheroo. In fact, when the external GPU is runtime suspended, > > > vga_switcheroo will cut power to the internal discrete GPU, resulting in > > > a lockup. > > > > I'm not necessarily opposed to this, but I'd prefer something more > > generic. E.g., what happens if someone uses another dGPU in a docking > > station or some other sort of PCIe bridge? > > Such a dGPU is only relevant to vga_switcheroo if it can either drive > the panel or be powered off by the platform. Does such a product exist? > > I've never heard of one, and think that's because such a product doesn't > make sense: A docking staton is not power-constrained, it's stationary > and connected to a wall outlet, so there's no need to power the dGPU off > when it's not in use. > > And at a docking station you're usually connected to a larger monitor, > so having the dGPU drive the laptop's smaller panel isn't necessary either. > In the rare cases where there's no larger monitor, you just use the dGPU > for render offloading, just as you would for contemporary ATPX laptops. > > OTOH, dGPUs in Thunderbolt enclosures *do* exist and connecting them > to an ATPX machine causes failure, as explained in the commit message. > > > > I think on AMD platforms > > at least we should be able to determine what devices are the > > switcheroo devices based on information in the ATIF and ATPX ACPI > > methods. In that case, we can be explicit in which devices we > > register with vga_switcheroo. > > Is there public documentation on these methods somewhere? The ACPI interface is documented in drivers/gpu/drm/amd/include/amd_acpi.h while drivers/gpu/drm/amd/amdgpu/amdgpu_atpx_handler.c contains some glue for ACPI and the amdgpu driver (similar code exists for radeon). -- Kind regards, Peter Wu https://lekensteyn.nl
