Looking for SGI Extreme graphics technical documentation

Hi,

I am looking for Extreme graphics technical documentation. Indigo2
PROM reports the graphics board as follows:

controller display SGI-GU1-Extreme key 0 ( ConsoleOut Output )
p: video(0)
 peripheral monitor key 0
 p: video(0)monitor(0)

So far I have been able to find some small bits of information,
including these ones:

http://en.wikipedia.org/wiki/Extreme_Graphics
http://www.futuretech.blinkenlights.nl/i2sec5.html#5.6
http://www.gossamer-threads.com/lists/gentoo/mips/58437
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/sgimips/gio/grtwo.c?rev=1.5.12.3&content-type=text/x-cvsweb-markup

These, however, do not seem to be enough to write a Linux console
driver, which is what I would like to do.

Can anyone help, please?

Thanks,
Dmitri