Creating a touch screen driver

[Søren Hauberg]

Hi All,
  Recently I've working on making a touchscreen work nicely on
GNU/Linux. By "nicely" I mean, the only needed configuration should be
the calibration, which shouldn't need to restart X. My first attempt
(which works great for me, btw) was to change the kernel module
'usbtouchscreen' to handle calibration. While it works for me, the
patch was not accepted upstream since it doesn't allow for multible
touchscreens to be attached to the same machine. So, now I guess I'll
have to write an X driver that'll handle the touchscreen. The kernel
module I'm targeting is using evdev, so that's the API I'll be working
against.
  So, my question is: should I attempt to extend the X11 evdev driver,
or should I create a new driver (from scratch?), or how should I
approach this problem? I guess I could also fork the 'evtouch' driver
that appears to be unmaintained.

Thanks,
Søren