I have to agree with jmk. Well written though many of the XFree86 drivers are,
they still contain a worrying number of comments along the lines of "I seem to
need to do this", or "this is opposite to what the manual says", or "dunno it
just seems to work". This is not the authors' fault, believe me.

Add to this that just because a driver covers all chip revisions, it doesn't mean
that it has actually been tested. You could sit down and transcribe all the good
looking stuff into Plan 9 and find it makes no difference at all.

This appears to be true for my laptop.

Moral is, try XFree86 _before_ copying the changes.