https://bugs.freedesktop.org/show_bug.cgi?id=75127
--- Comment #7 from Alex Deucher agd5f@yahoo.com --- (In reply to comment #6)
Compiled and installed Linux 3.12.12 kernel. No GPU hang problems occur for suspend and resume. Works fine (other than the fact that the laptop's display connected through LVDS is blank).
Does disabling dpm help? Boot with radeon.dpm=0 on the kernel command line in grub. If not, can you bisect the kernel with git to find out what commit caused the regression?