Comment # 8 on bug 79338 from José Suárez

Finally the problem I was experiencing was indeed related to the linux kernel.
I have installed 3.15-rc7 (I which I had not updated since rc6) and the
problems are gone. Not sure why, but the newer llvm revisions were triggering
the bug more frequently.

Guessing by the 3.15-rc7 changelog, I was probably affected by a drm bug:

Alex Deucher (4):
      drm/radeon: fix DCE83 check for mullins
      drm/radeon: handle non-VGA class pci devices with ATRM
      drm/radeon: fix register typo on si
      drm/radeon/pm: don't allow debugfs/sysfs access when PX card is off (v2)

This report may now be closed.

Thank you, Michel, for your help.