Re: [PATCH 1/2] HID: multitouch: report MT_TOOL_PALM for non-confident touches

From: Henrik Rydberg
Date: Fri Jun 01 2018 - 15:19:21 EST

However, I interpret a firmware that send (confidence 1, tip switch 1)
and then (confidence 0, tip switch 0) a simple release, and the
confidence bit should not be relayed.
This unfortunately leads to false clicks: you start with finger, so
confidence is 1, then you transition the same touch to palm (use your
thumb and "roll" your hand until heel of it comes into contact with the
screen). The firmware reports "no-confidence" and "release" in the same
report and userspace seeing release does not pay attention to confidence
(i.e. it does exactly "simple release" logic) and this results in UI
interpreting this as a click. With splitting no-confidence
(MT_TOOL_PALM) and release event into separate frames we help userspace
to recognize that the contact should be discarded.
This is in part why I objected to this patch on August 11th, 2017. Logically, the confidence state is a property of a contact, not a new type of contact. Trying to use it in any other way is bound to lead to confusion.