https://bugs.freedesktop.org/show_bug.cgi?id=91486
--- Comment #2 from Mike Lothian mike@fireburn.co.uk --- I'm going to try an older kernel just in case but I'm worried this might be hardware failure
The last time I booted up X would start but then the machine would freeze up
Had to boot with radeon.dpm=0 radeon.runpm=0 radeon.modeset=0 to get X to start