Comment # 2 on bug 82201 from Alex Deucher

Please attach your dmesg output with radeon.dpm=1 set on the kernel command
line in grub.  That dumps some additional debugging output.  Also please attach
a copy of your vbios.

(as root)
(use lspci to get the bus id)
cd /sys/bus/pci/devices/<pci bus id>
echo 1 > rom
cat rom > /tmp/vbios.rom
echo 0 > rom