Comment # 1 on bug 91880 from Alex Deucher

It's supported.  Please attach your xorg log, dmesg output and a copy of your
vbios.  To get 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