I tried booting with radeon.dpm=1 with Mageia 4 beta 2 (kernel-3.12.5 &
mesa-10.0).
Gfx cards is RV670 ([Radeon HD 3690/3850], PCI ids: vendor=1002 device=9505
subv=174b subd=2542)

First xorg often results in black screen then gnome failure.
Subsequent xorgs are slow to death

dmesg is filled with:
+*ERROR* atombios stuck in loop for more than 5secs aborting
+*ERROR* atombios stuck executing CE58 (len 349, WS 0, PS 4) @ 0xCE75

or:
+*ERROR* atombios stuck in loop for more than 5secs aborting
+*ERROR* atombios stuck executing CDBE (len 153, WS 0, PS 4) @ 0xCDD4
+*ERROR* atombios stuck executing B9E2 (len 760, WS 0, PS 0) @ 0xBB6B
+*ERROR* atombios stuck executing B920 (len 138, WS 0, PS 8) @ 0xB92A