[PATCH/WIP xf86-input-libinput 0/3] Add tablet support

[Peter Hutterer]

This patchset adds tablet support to the xorg libinput driver.
Note: this patchset requires the tablet-support branch of libinput, the
current tree for this patchset is avaiable here:
https://github.com/whot/xf86-input-libinput/tree/wip/tablet-support

I'm sending this to the list mostly to get a few eyes and comments on the
general approach here.

The wacom driver is the most complicated of all X.Org drivers, in part
because tablets are just more complicated than say a mouse/keyboard but also
because it accumulated 15 years of legacy that is hard to remove. But in the
15 years we've had a fair number of improvements, both in hardware and the
kernel so a lot of hacks and workarounds simply aren't needed anymore.

The biggest difference here is that we create X devices on the fly as they
come into proximity, one per tool. Static InputDevice configuration in the
xorg.conf becomes mostly useless this way (InputClass still works), it's
better to have a DE that knows about and handles tablets.

No new config options at this point, the libinput tablet branch doesn't
expose any of those. This probably won't work yet with the cursor/lens
cursor tool, hence all still WIP.

Cheers,
  Peter