Created attachment 78069 [details]
lspci

This happens always with KDM, LightDM/XDM (xdm-archlinux package). Login screen
freezes (but I can move mouse pointer).

First I thought that was my configuration error but the same issue with knoppix
livecd (7.0.5, kernel 3.6.10, mesa-9.0.1)

Without Display Manager (startx from console) result is the same. Screen
appears but is frozen (test using xfce4 and kde). Without DM I don't see any
GPU lockup but Xorg.0.log shows errors.

Setting R600_HYPERZ=0 or R600_DEBUG=nohyperz doesn't help

system
kernel 3.8.5 or 3.9.0-rc7
mesa 9.1.1 
other packages are up to date form arch repository