Comment # 101 on bug 66963 from Alex Deucher

(In reply to comment #96)
> Not so fast fellas. Recently checked 3.11RC7 and DRM-Next (current). The
> result is the same: it still can't boot with my Radeon HD 2600 XT :(

Does disabling aspm help?  `radeon.aspm=0 radeon.dpm=0` on the kernel command
line in grub.