R9285 agd5f drm-next-4.9-wip since 

commit c04399f19436616875879ee2711c5b78a90dd1b0
Author: Rex Zhu <Rex.Zhu@amd.com>
Date:   Thu Aug 18 18:27:14 2016 +0800

    drm/amdgpu: add vce bypass mode for tonga.

    fix issue that encode test failed on the second time when
    vce dpm enabled on tonga.

vce clocks seem stuck low, forcing gpu perf to high doesn't help.

500 frames 2160p nv12 from/to ram.

omx 8 seconds -> 35

vaapi 12 seconds -> 51