https://bugzilla.kernel.org/show_bug.cgi?id=91571
--- Comment #2 from Alex Deucher alexdeucher@gmail.com --- Both fglrx and radeon support dynamic power management so this does not likely have anything to do with power management. It looks like a plain old GPU hang. I'd suggest updating your mesa stack in the case of the open source driver. It's more likely a bug in mesa than a kernel driver bug.