(In reply to Alex Deucher from comment #2)
> Can you bisect?

No need: most likely, the offending commit is 8a357d10043c ("drm: Nerf
DRM_CONTROL nodes").

C.f. the discussion at
http://lkml.kernel.org/r/20161203144700.2307-1-nicstange@gmail.com

A patch for amdgpu is in the works as well.