Comment 11 for bug 982415

Incoherent batch buffer, sounds like another instance of:

commit 14667a4bde4361b7ac420d68a2e9e9b9b2df5231
Author: Chris Wilson <email address hidden>
Date: Tue Apr 3 17:58:35 2012 +0100

    drm/i915: Finish any pending operations on the framebuffer before disabling

    Similar to the case where we are changing from one framebuffer to
    another, we need to be sure that there are no pending WAIT_FOR_EVENTs on
    the pipe for the current framebuffer before switching. If we disable the
    pipe, and then try to execute a WAIT_FOR_EVENT it will block
    indefinitely and cause a GPU hang.