I get loads of these in dmesg:
[950253.948694] radeon 0000:04:00.0: Packet0 not allowed!
For debugging purposes: mesa-git.2014-07-03 llvm-3.4.2 linux-3.16-rc3 xf86-video-ati-7.4.0 xorg-server-1.14.2 glamor-egl-0.6.0
04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Oland PRO [Radeon R7 240]