https://bugs.freedesktop.org/show_bug.cgi?id=83708
--- Comment #12 from Michel Dänzer michel@daenzer.net --- (In reply to comment #9)
radeon:GPU lockup cp stall for ... more than...
That means the GPU hangs while processing commands, probably because the commands are malformed in some way (e.g. wrong byte order).
Please attach the exact changes you've made to get to that point.