According to my tests this nasty bug (which I observed mainly with VirtualBox and OS/2 guest) has been fixed with the recent kernel update in Wheezy to 3.2.0-51.
My guess is this commit which cured the freezes: commit 884020bf3d2a3787a1cc6df902e98e0eec60330b upstream. After any "soft gfx reset" we must manually invalidate the TLBs associated with each ring. Empirically, it seems that a suspend/resume or D3-D0 cycle count as a "soft reset". The symptom is that the hardware would fail to note the new address for its status page, and so it would continue to write the shadow registers and breadcrumbs into the old physical address (now used by something completely different, scary). Whereas the driver would read the new status page and never see any progress, it would appear that the GPU hung immediately upon resume. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org