On 02/02/17 12:59 AM, Arnd Bergmann wrote: > My randconfig tests on linux-next showed a newly introduced warning: > > drivers/gpu/drm/amd/amdgpu/amdgpu_object.c: In function 'amdgpu_bo_create_restricted': > drivers/gpu/drm/amd/amdgpu/amdgpu_object.c:377:2: error: #warning Please enable CONFIG_MTRR and CONFIG_X86_PAT for better performance thanks to write-combining [-Werror=cpp] > > Generally speaking, warnings about bad kernel configuration are not particularly > helpful. We could enforce the selection of X86_PAT through Kconfig, so the driver > cannot even be used unless it is enabled, Making AMDGPU depend on X86_PAT would be wrong I think, and any fancier Kconfig solution might be overkill. > or we could just rely on the runtime warning that is also there. That might make sense, since the runtime warning is only triggered when the lack of PAT actually makes a difference. OTOH the people running the kernel aren't always the same people building it, so the downside is that this would potentially delay getting X86_PAT enabled. > In this version, I'm making the warning conditional on CONFIG_COMPILE_TEST, which > shuts it up for me, but not people that may actually want to run the kernel > as a compromize. This is fine with me as well. Whichever way we end up going for this, it should be applied to the radeon driver as well. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer
