hid-uclogic should set Pen or Digitizer, depending on usage

[whot]

Filing this mostly so there's a record somehere.

The report descriptor fixup uclogic_rdesc_v1_pen_template_arr sets Usage (Digitizer) but the kernel differs between "Digitizer" (for external tablets, INPUT_PROP_POINTER) and "Pen" for display tablets (INPUT_PROP_DIRECT). Userspace somewhat relies on INPUT_PROP_DIRECT to know if we're dealing with a direct-input device (see libinput!1019 for a workaround).

Ideally uclogic would set pen vs depending on the device, though I understand that's not exactly trivial in the current implementation.

[JoseExposito]

As far as I know, there is no information in the tablet or pen descriptor (uclogic_params_pen_init_v2) to differentiate them. Here are a couple of examples of INPUT_PROP_DIRECT devices:

• Huion Kamvas Pro 13 & Raspbian - Tilt, pressure etc... detected by xinput/evtest/debugfs but not by apps #633
  S C8 13 03 80 E5 00 18 81 00 FF 1F D8 13 03 05 00 01 08 00 40
• Huion Kamvas 20 (GS1901) Support #560
  S C8 13 03 BA 53 01 88 BA 00 FF 1F D8 13 03 00 00 00 08 00 40

The only way to differentiate them is creating a list of devices with screen in the kernel... But that's already done in libwacom, so your solution works pretty well.
If a kernel fix is really needed, I can work on one, but I don't think it is worth it.

Leaving this bug open, as it is not fixed here, but most likely, we won't see a fix in the kernel any time soon.

[whot]

we already map the firmware to the uniq here, right? so it would be relatively trivial to generate a firmware id to internal/external mapping from libwacom and add that here. But yeah, ETIME and EMOTIVATION :)

[JoseExposito]

Class=Cintiq and IntegratedIn=Display is already set in libwacom for Kanvas devices. The privative driver exposes that information, so I think that no further changes are required :D