Comment # 11 on bug 104306 from Sergey Kvachonok

I can confirm that switching from radeon to amdgpu on

03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Pitcairn XT [Radeon HD 7870 GHz Edition]

Device: AMD Radeon HD 7800 Series (PITCAIRN / DRM 3.19.0 / 4.14.11-1-ARCH, LLVM
5.0.1) (0x6818)

fixes the issue.