Comment # 3 on bug 43248 from BDM

I'm having the same problem with the same dmesg output with the same chipset
HD6520 for any game that sets true full screen graphics mode on Ubuntu 12.10.
If I use a game, like Titanion, that can be closed by simple keystrokes, I can
manage to escape the black screen and get back to my normal desktop. 

Also perhaps unrelated, setting to a lower resolution desktop mode 800x600, or
lower seems to set an incorrect mode that garbles the screen. That too I can
escape if I have an xrandr ready to enable me to do so. 

Here's uname -a

Linux falcon 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:31:23 UTC 2012 x86_64
x86_64 x86_64 GNU/Linux

Relevant part of dmesg
[  681.224351] [drm:atom_op_jump] *ERROR* atombios stuck in loop for more than
5secs aborting
[  681.224364] [drm:atom_execute_table_locked] *ERROR* atombios stuck executing
E2F6 (len 2585, WS 4, PS 4) @ 0xE9E0
[  681.259083] [drm:radeon_dp_link_train_cr] *ERROR* clock recovery reached max
voltage
[  681.259095] [drm:radeon_dp_link_train_cr] *ERROR* clock recovery failed

I think the driver is partially broken for this chipset.