This commit was borrowed from uxa driver contributed by Eric.
commit number is e0066e77e026b0dd0daa0c3765473c7d63aa6753. commit log paste as
below:
We were clipping each span against the bounds of the clip, throwing
out the span early if it was all clipped, and then walked the clip box
clipping against each of the cliprects. We would expect spans to
typically be clipped against one box, and not thrown out, so we were
not saving any work there. For multiple cliprects, we were adding
work. Only for many spans clipped entirely out of a complicated clip
region would it have saved work, and it clearly didn't save bugs as
evidenced by the many fix attempts here.
Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
ba6dd8aa49