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

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Message-ID: <CAO-hwJKibKvqviLZ5SSYR_X3yLTzJrr0G4d6svM3FtgJ6AfvQQ@mail.gmail.com>
Date:   Mon, 4 Jun 2018 14:57:54 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Henrik Rydberg <rydberg@...math.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        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

On Fri, Jun 1, 2018 at 9:03 PM, Henrik Rydberg <rydberg@...math.org> wrote:
>
>>> 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.

Problem is that MT_TOOL_PALM has been introduced in the kernel since
v4.0 (late 2015 by a736775db683 "Input: add MT_TOOL_PALM").
It's been used in the Synaptics RMI4 driver since and by hid-asus in late 2016.
I can't find any other users in the current upstream tree, but those
two are already making a precedent and changing the semantic is a
little bit late :/

Cheers,
Benjamin

>
> Henrik
>