https://bugs.freedesktop.org/show_bug.cgi?id=30007
--- Comment #3 from Marek Olšák maraeo@gmail.com 2010-09-11 08:52:26 PDT --- A black area? It looks like a shader fail to compile. The driver always prints some info to stderr if anything goes wrong.
Can you somehow get the stderr output?
Also, is there anything in dmesg?