Hi, surprised I haven't seen any mention of this yet, but according to here: GMA500 staging driver Alan Cox has cobbled together a driver.

This is an initial staging driver for the GMA500. It's been stripped out
of the PVR drivers and crunched together from various bits of code and
different kernels.

Currently it's unaccelerated but still pretty snappy even compositing with
the frame buffer X server.
Original thread here: http://thread.gmane.org/gmane.linux.kernel/1103793