https://bugs.freedesktop.org/show_bug.cgi?id=75357
--- Comment #11 from Michel Dänzer michel@daenzer.net --- (In reply to Nix from comment #10)
FWIW, I have just started seeing behaviour very similar to this, also with an HD6850, though it is probably a distinct bug because all the software versions involved are very different.
So it would probably be better to file your own report.
This happened after closely-adjoined upgrades of the kernel (from 3.19 to 4.0.3), the X server (from 1.15.1, yes, I know, it's because of the security holes I finally upgraded, to 1.17.1), the ATI driver (from 7.3.0-26 to 7.5.0.68, all "git describe" output from the unmodified trunk), Mesa (from 10.2.6 to 10.5.5), and LLVM (from 3.3 to 3.5.2), so the fault could, alas, in theory lie in any or all of these.
It would be great if you could narrow that down a bit. The r600g driver doesn't use LLVM, so that's probably not it. I agree it's most likely between Mesa or the kernel, or maybe xf86-video-ati.
Glamor is not in use.
Have you tried glamor to see if it happens with that as well?
Does
Option "ColorTiling2D" "off"
in /etc/X11/xorg.conf or the environment variable R600_DEBUG=no2d (or even R600_DEBUG=notiling) for chromium work around the problem?
dpm is, and has been working flawlessly thank you very much, cutting my desktop's power consumption from 130W to 90W :) over the last year that's saved at least the price of the beer I owe you for the dpm work, Michel :)
Sounds great, but I haven't done any DPM work, I think that beer would have to go to Alex. :)