Comment # 5 on bug 91893 from macro@hotmail.com

Kernel arguments:

radeon.no_wb=1
radeon.dynclks=0
radeon.agpmode=-1
radeon.gartsize=32
radeon.msi=0
radeon.dpm=0
radeon.aspm=0
radeon.runpm=0
radeon.hard_reset=1
radeon.use_pflipirq=0
radeon.bapm=0

One or more (not sure exactly which) are required in order for X to start
without hanging the machine.