Comment 80 for bug 78684

I found a possible solution:

http://wiki.archlinux.org/index.php/ATI_Radeon_&_Kernel_2.6 (see hardware conflicts section)
http://forums.gentoo.org/viewtopic-p-3954435.html
http://bugzilla.kernel.org/show_bug.cgi?id=6350

At the moment it seems that downgrading bios or patching the kernel is the only solution.