https://bugs.freedesktop.org/show_bug.cgi?id=69694
--- Comment #17 from Marco mpiazza@gmail.com ---
Are you sure it doesn't work if you remvoe your xorg.conf completely?
Yes, I'm sure. Without a xorg.conf I only have a black screen with the cursor caret in the upper left corner.
I also tried disabling dpm (radeon.dpm=0) but the result is the same.
I think the problem is due to having two gpus under radeon driver and glamor.