https://bugs.freedesktop.org/show_bug.cgi?id=65963
--- Comment #21 from paul.woegerer@gmail.com --- (In reply to comment #20)
(In reply to comment #19)
@Damian, I had the same problems. My configuration is similar to yours: Radeon 7870, Linux 3.16.1, xorg 1.16, MESA 10.3 RC1 (fedora f21 branch).
After consulting https://wiki.archlinux.org/index.php/ATI it tried adding radeon.dpm=0 to my kernel command line as a workaround. It solved the problem. No more lockups. The system is now stable with the above configuration. Clearly this has something to do with the powermanagement changes in MESA and the kernel (there were no lockups with earlier versions of MESA)
There is no power management code in mesa. Power management is completely self-contained in the kernel. If you are not getting lockups with dpm enabled and an older version of mesa, it may be a mesa issue.
Hmm, sounds like newer versions of MESA trigger a dormant power management issue in the radeon kernel driver (with certain Pitcairn hardware) ...just speculating.
It's a while ago thus I can't tell the exact version of kernel and MESA when I first observed the behavior. All I can say for sure is that now since using radeon.dpm=0 I did not experience a single lockup anymore (which is good enough for me).
Is there a way to build the radeon kernel driver with some additional debugging/logging that could help you to understand what's going on ?