https://bugzilla.kernel.org/show_bug.cgi?id=68571
--- Comment #83 from Michel Dänzer michel@daenzer.net --- (In reply to Weber K. from comment #81)
And since I put this in grub.cfg and fstab, never had a black screen again: rootflags=relatime,lazytime,commit=60 iommu=noagp radeon.dpm=1
It could be iommu=noagp, at least that would make more sense than filesystem flags...