Comment 20 for bug 68433

I think this is problem is not related to #28925, changing xorg.conf to use the "radeon" driver instead of "ati" would not have helped otherwise. This seems to be related to not properly detecting the gfx chipset in the first place. The Xorg.0.log suggests that something goes wrong when detecting the gfx chipset. It might be useful to checkout bugs.freedesktop.org in order to find out whether upstream knows about this or not.