HID: wacom: Correct behavior when processing some confidence == false…

[flying-elephant]

… touches

There appear to be a few different ways that Wacom devices can deal with confidence:

1. If the device looses confidence in a touch, it will first clear the tipswitch flag in one report, and then clear the confidence flag in a second report. This behavior is used by e.g. DTH-2452.

2. If the device looses confidence in a touch, it will clear both the tipswitch and confidence flags within the same report. This behavior is used by some AES devices.

3. If the device looses confidence in a touch, it will clear only the confidence bit. The tipswitch bit will remain set so long as the touch is tracked. This behavior may be used in future devices.

The driver does not currently handle situation 3 properly. Touches that loose confidence will remain "in prox" and essentially frozen in place until the tipswitch bit is finally cleared. Not only does this result in userspace seeing a stuck touch, but it also prevents pen arbitration from working properly (the pen won't send events until all touches are up, but we don't currently process events from non-confident touches).

This commit centralizes the checking of the confidence bit in the wacom_wac_finger_slot() function and has 'prox' depend on it. In the case where situation 3 is encountered, the treat the touch as though it was removed, allowing both userspace and the pen arbitration to act normally.

Fixes: 7fb0413baa7f ("HID: wacom: Use "Confidence" flag to prevent reporting invalid contacts")
Cc: stable@vger.kernel.org

Link: https://lore.kernel.org/all/20231219213344.38434-1-jason.gerecke@wacom.com/
[tatsunosuke.tobita@wacom.com: Imported into input-wacom (502296030ec6)]

[Pinglinux]

Thank you Tats for your effort!