If they're using the pro driver (dkms + closed GL/etc) there are known issues with CGCG and the UMD. Try booting with amdgpu.cg_mask=0xFFFFFFFB to disable CGCG. Note this will also disable power gating so battery life/temp might be an issue :-/ I unfortunately don't have an 88xx series Carrizo (mine is an A12-9800) and with the all open UMD I haven't noticed any problems with PG/CG. Nicolai has an 8800 I think we should involve him here.