https://bugs.freedesktop.org/show_bug.cgi?id=95015
--- Comment #4 from Oded Gabbay oded.gabbay@gmail.com --- Did you try running a 4.5 kernel ? I added a POWER relevant fix for radeon in 4.5, which relates to caches (c524498 - drm/radeon: mask out WC from BO on unsupported arches)