Radeon KMS not working

[ravi at p-static.net]

I've been working on a Radeon KMS setup since yesterday, and I've finally
got it to the point where nothing works at all. :) At this point, the
error I get is that when I try to start X, video card tops outputting any
signal at all, and I get the following lines in my /var/log/messages a few
dozen times a second:

[drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(5).
[drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !

I'm using linux-2.6.31-rc8, and mesa, xorg-server, and xf86-video-ati from
git checkouts from yesterday, as well as git versions of a few other
libraries (I can provide exact versions and revision numbers for
everything if necessary, but I don't know what all is relevant right now).

Normally I'd assume it's a transient issue, since I'm running several
things from git, but [1] indicates that people have been seeing this same
error for several months now.

[1]: http://www.phoronix.com/forums/showpost.php?p=77860&postcount=8

Also, I tried disabling KMS in the kernel once I got everything installed
(radeon.modeset=0 as a kernel parameter), hoping that everything would
fall back on the old code paths and work again - unfortunately, it still
crashed immediately. Should I have expected this to work?

--Ravi