[PATCH 00/13] Revamp touchpad acceleration code

[Peter Hutterer]

This patchset is a cleanup and revamp of the touchpad acceleration code.
It doesn't give us perfect acceleration, but it goes from the current rather
abysimal state to one that should at least be good enough most of the time.
More tweaking will come, but meanwhile santa and whatnot.

Right now, we use the mouse acceleration for touchpads with a magic slowdown
applied. The first 10 patches separate the touchpad code from the mouse
acceleration code and switch it to use mm/s as base velocity unit (rather
than the current 1000dpi-mouse-equivalency units). 11 is the main change
that changes the acceleration pattern, mostly to start accelerating at a lot
higher finger speed (found mostly by trial and error). See that patch for
details. 12 is the doc update, 13 is a gratitous change that just seems to
make it feel better, but who knows.

Some pretty graphics and writeup
http://who-t.blogspot.com/2016/12/libinput-touchpad-pointer-acceleration.html

Branch is available here:
https://github.com/whot/libinput/tree/wip/touchpad-pointer-accel-v3
but beware, it spews debug printfs like crazy. Just reset back a few
commits if you're trying this branch.

Cheers,
  Peter