Display corruption on 1.8.0/Mesa 7.8

[Marty Jack]

I'm having a nasty amount of corruption on DG965WH, Linux 2.6.33.2, xorg-server 1.8.0, Mesa 7.8, libdrm 2.4.20.  The same with 1.7.6 and 7.7 works fine.  All built from release tarballs and unmodified (except a two-line backport of symbols KMS_BO_TYPE_CURSOR_64X64_A8R8G8B8 and KMS_BO_TYPE_SCANOUT_X8R8G8B8 to get 7.7 to compile against 2.4.19/20).

Most things are okay.  I am experiencing a lot of corruption on vertical scrolling; some rectangular areas of the display don't redraw.  This is particularly ugly when editing a source file, because I am never sure where I am clicking or selecting.  It is most noticeable on a small scroll such as you get with the scroll wheel.  I see it also when scrolling a web page in a browser.  It tends to be reproducible if you scroll down and then up one scroll wheel click.  If I bring up a .jpg in the browser, I get some rectangular areas where the image is white.  If I then do a "back" and "forward" to get it redrawn, it is completely drawn.  I know this is not the best description, but I am looking for guidance on where to look first.

I have had to revert this to 1.7.6/7.7 in order to keep working, but if anyone has an idea which component it is, I could do some bisecting; unless someone has an aha! moment and can solve it just from the description.