[RFC libinput 0/9] touchpad: force resolutions for all touchpads

[Peter Hutterer]

Not all touchpads provide x/y axis resolution. some of them (apple
touchpads) we fix up in the systemd hwdb but others are harder to detect or
fix in a generic manner. so we set a fake resolution (1 unit/mm), but that's
just to avoid divide-by-zero.

the touchpad code handles physical distances where possible but always has
an escape path to handle the resolution-less touchpads, most of that by some
magic numbers or percentages but those may or may not be correct. especially
on the touchpads we don't have available for testing we have no idea how
close the behaviour is to the intended one.
 
this patchset does away with the fake resolution handling. a udev callout
checks for the firmware version and assigns a tag based on that, the hwdb we
ship then assigns size hints for the device. anything that doesn't get a
size hint is simply set to a default size.
this may make some touchpads worse in the short term, but long term we
should be able to narrow down the various sizes and provide hwdb entries for
them - and get the same behaviour across devices.

Note that the hwdb entries are just approximates so far, the ALPS fw version
8 is a measurement of such a device, everything else is just assumption or
blind guesses. I'll try to collect some real-world sizes before pushing
this if we're happy with this approach.

1/9 and 2/9 are independent and can go in regardless.

Cheers,
  Peter