https://bugzilla.kernel.org/show_bug.cgi?id=37112
--- Comment #5 from Hrvoje Senjan hrvoje.senjan@gmail.com 2011-06-11 06:45:28 --- My first guess is , that kernel changes memory clock too low - with fglrx lowest memory clock is at 400MHz , but with radeon module/low frequency it changes it to 300MHz.
dri-devel@lists.freedesktop.org