i915_vblank_tasklet: Try harder to avoid tearing.

Previously, if there were several buffer swaps scheduled for the same vertical
blank, all but the first blit emitted stood a chance of exhibiting tearing. In
order to avoid this, split the blits along slices of each output top to bottom.

Signed-off-by: Dave Airlie <airlied@linux.ie>
1 file changed