https://bugs.freedesktop.org/show_bug.cgi?id=44772
--- Comment #6 from Harald Judt h.judt@gmx.at 2012-03-20 11:15:35 PDT --- The bug is still present with kernel-3.3 final.
Further tests confirm that this is an issue specific to the HD6950 card. I swapped the card with a Radeon HD3650 (RV635 chipset) for testing while leaving the rest of the system configuration unchanged, and the problem was no longer reproducible and hibernating and resuming worked fine.
If I change the power profile back from low to default, sometimes the system will freeze immediately when hibernating. Maybe some registers still don't get initialized/updated properly?