With Linux 4.5-rc3 having some notable AMDGPU fixes, I spun a new kernel locally for my benchmarking of it and have again made it public for the lack of an easy Ubuntu kernel exposing these options. For using the AMDGPU PowerPlay feature on a supported GPU, you still need to boot your kernel with amdgpu.powerplay=1 as the feature isn't otherwise enabled by default at runtime on Linux 4.5. If wanting to test the AMDGPU CIK experimental support for GCN 1.1 GPUs like the R9 290 series, you need to blacklist the Radeon DRM driver so it won't load before the AMDGPU DRM driver has a chance to tap the card.
If you aren't familiar why the AMDGPU PowerPlay support is critical, you certainly aren't reading enough Phoronix and should check out many of the past PowerPlay articles and benchmarks as this is crucial for getting good open-source performance on GCN 1.2+ GPUs like the R9 285 Tonga and R9 Fury.
You can download this Linux 4.5-rc3 Ubuntu kernel spin with the AMDGPU PP+CIK enabled (aside from those Kconfig options enabled, it's close to a default Ubuntu kernel configuration) over on Phoronix.net. I'll have more open-source Linux graphics tests from this latest code and Mesa Git on Phoronix in the coming days.