Bug 11787

my machine is IBM ThinkPad T43p [ATI FireGL M24 GL 3154 (PCIE)], but other people report this with different hardware, the issue seems to be the same as reported here: http://lists.freebsd.org/pipermail/freebsd-questions/2003-September/019065.html
here:
http://lists.freebsd.org/pipermail/freebsd-x11/2006-May/002926.html
here:
http://archive.netbsd.se/?ml=freebsd-multimedia&a=2006-02&t=1781223
and here:
http://forums.pcbsd.org/viewtopic.php?p=43974&sid=f5e235d25315c50a686e5e8e4dd799ba
...among other places.

what seems to be happening is that card's FIFO gets full and X.org gets stuck calling DRM_IOCTL_RADEON_CP_IDLE that keeps returning EBUSY and never succeeds.
what is interesting, though, is that in 2 out of [many] tries X.org did actually manage to start and worked fine from then on until next reboot. so it seems to be intitialization issue. perhaps a race of some kind?
anyway, i recompiled the kernel with DRM_DEBUG, enabled RADEON_FIFO_DEBUG in radeon_cp.c and got some debug info[1] which may be useful. complete Xorg.0.log is also available[2].
the visible effect is that the video mode changes, but the screen stays blank.
machine is responsive, sshd works, but switching virtual consoles is not possible.
i am very much willing to assist with applying patches and providing more info.

[1] http://rojer.pp.ru/misc/radeon_DRM_DEBUG.log
[2] http://rojer.pp.ru/misc/radeon_drm_Xorg.0.log