When it hangs (which always happen if I don't have X already started), I
sometimes get a bunch vertical white and black stripes. dmesg doesn't show
anything interesting, just

[  278.575937] fbcon: radeondrmfb (fb0) is primary device
[  278.590490] Console: switching to colour frame buffer device 240x67
[  278.602467] radeon 0000:01:00.0: fb0: radeondrmfb frame buffer device
[  278.602531] radeon 0000:01:00.0: registered panic notifier
[  278.606539] [drm] Initialized radeon 2.37.0 20080528 for 0000:01:00.0 on
minor 0