The SDL-based game "teeworlds" crashes on a laptop with Radeon IGP 330M/340M/350M [1002:4337] when KMS is used, but it runs fine when I use "nomodeset".
When I don't have "firmware-linux-nonfree" installed the game also doesn't crash but it's 20 times slower, about 1 fps.
I tested on many recent Debian and Ubuntu versions - the output below is from Debian testing (Wheezy). I had to comment out "options radeon modeset=1" in /etc/modprobe.d/radeon-kms.conf for "nomodeset" to take effect.
I can attach more output upon request, or test with different software versions.
<unrelated game output>
drmRadeonCmdBuffer: -22. Kernel failed to parse or rejected command stream. See dmesg for more info.
$ dmesg | tail -n 2
[ 355.980790] [drm:r100_cs_track_texture_check] *ERROR* No texture bound to unit 0
[ 355.980838] [drm:radeon_cs_ioctl] *ERROR* Invalid command stream !
$ lspci -nn -k | grep -A 2 VGA
01:05.0 VGA compatible controller : ATI Technologies Inc Radeon IGP 330M/340M/350M [1002:4337]
Subsystem: Compaq Computer Corporation Device [0e11:0056]
Kernel driver in use: radeon
$ dpkg-query -W xserver-xorg-video-radeon firmware-linux '*mesa*'
$ uname -a
Linux myrto 2.6.38-2-686 #1 SMP Sun May 8 14:49:45 UTC 2011 i686 GNU/Linux