Comment # 15 on bug 95017 from erhard_f@mailbox.org

Played around a bit with xorg and kernel options on my G5 and worked out that I
can drive the Radeon 9650 at AGP x8 if I disable DRI completely via Option
"NoAccel" "true" in /etc/xorg.conf.

I had no GPU-lockups since then and xorg is much more responsive despite
lacking DRI hardware acceleration (radeon.agpmode=-1 with DRI enabled).