How do I restart the GPU from command line?

Using a HP DV6 laptop with Ubuntu 12.04-64 and an ATI mobile GPU. Installed the standard ATI propriety drivers suggested by Ubuntu. When I close the lid, the computer goes down to suspend mode. When open the lid, everything but the screen resumes again. Just black. I'll guess I have to put a GPU reset script in `/etc/pm/sleep.d`. But how do I restart/reset the GPU?