My main gripe with the AMDGPU DRM driver is that it hasn't supported re-clocking / power management for the discrete graphics cards like the Radeon R9 285 and R9 Fury. Without it, the performance is terribly slow. Fortunately, these PowerPlay patches are finally providing the support albeit it will be a few months before seeing the code in a released Linux kernel.
What the Linux desktop looked like when PowerPlay support first came to ATI Catalyst on Linux.
Implementing PowerPlay support for the AMDGPU driver took 51 patches from multiple AMD developers. This power management code amounts to about 45 thousand lines of new code.
The patch series in its current form can be found via the DRI-devel mailing list. The patches can also be tried via this Git branch.
Due to the timing, this AMDGPU PowerPlay support won't be landing until the Linux 4.5 kernel. However, as soon as time allows I intend to carry out some AMDGPU benchmarks vs. Catalyst with this code on Tonga and Fiji.