https://bugs.freedesktop.org/show_bug.cgi?id=27644
--- Comment #11 from Oliver Joos oliver.joos@freenet.ch 2011-01-27 11:03:36 PST --- Seems I have the same problem with an ATI X600 (chipset RV380) in my laptop HP Compaq nx8220. Same symptoms and the kernel parameters "radeon.modeset=0 vga=771" also fixed it finally, whereas "radeon.new_pll=0" alone did not help (another dozen of googled suggestions failed too. So many thanks for this hint!)
My graphics adapter: 01:00.0 VGA compatible controller: ATI Technologies Inc M24 1P [Radeon Mobility X600]
I use Ubuntu Lucid with kernel 2.6.35-23 and disabled KMS ever since, because with KMS overlay video playback is not possible anymore and textured video playback shows artifact (looks like a diagonal edge of an OpenGL triangle not drawn correctly synchronized with vsync. But thats another bug...).
If I can help with further data or tests, then please just ask.