[Intel-gfx] Flickering i915

[Chris Wilson]

I'm experiencing a flicker (a horizontal shift) on the display with
every execution of a batchbuffer, using an i915 with .31-rc5 +
drm-intel-next.

Git bisect points to:
commit 920338ec20c06452dbdc24336ce4a6a8b86fb682
Author: Jesse Barnes <jbarnes at virtuousgeek.org>
Date:   Tue Jul 14 10:15:56 2009 -0700

    drm/i915: FIFO watermark calculation fixes
    
And I verified that the problem still occurs with both of Jesse's later
fixes applied.
-ickle