Missing dial support for Huion Q620M and other graphical tablets
Summary
Many Huion tablets feature a dial, it's a very convenient encoder that's for all intents and purposes is an extra set of buttons. It generates button presses when rotated clockwise or counterclockwise. Currently, dials are missing from libinput entirely.
Affected Hardware
Huion Q620M and potentially other Huion devices with a dial
Implementation in Other Systems
There is a userspace driver that uses hidraw, Huion-keys. It's a fairly straightforward implementation. I'm not familiar with libinput, so I don't know if there should be a specific pad_dial code or it could be just added to the buttons because these are essentially just buttons.