linux-kernel - Re: [PATCH 1/2] HID: multitouch: report MT_TOOL

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Date:   Fri, 1 Jun 2018 21:03:21 +0200
From:   Henrik Rydberg <rydberg@...math.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Jason Gerecke <killertofu@...il.com>,
        Dennis Kempin <denniskempin@...gle.com>,
        Andrew de los Reyes <adlr@...gle.com>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] HID: multitouch: report MT_TOOL_PALM for
 non-confident touches


>> 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.

Henrik