linux-kernel - Re: [PATCH 0/1] Do not map BTN

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Date:   Wed, 1 Dec 2021 15:56:41 +1000
From:   Peter Hutterer <peter.hutterer@...-t.net>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     José Expósito <jose.exposito89@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/1] Do not map BTN_RIGHT/MIDDLE on buttonpads

On Wed, Nov 24, 2021 at 10:39:02AM +0100, Benjamin Tissoires wrote:
> Hi José,
> 
> On Tue, Nov 23, 2021 at 8:12 PM José Expósito <jose.exposito89@...il.com> wrote:
> >
> > Hi all,
> >
> > Historically, libinput has relayed on the INPUT_PROP_BUTTONPAD property
> > to detect buttonpads.
> >
> > Since buttonpads are expected to have only one button (BTN_LEFT),
> > recently we added a new rule to detect buttonpads: Where a touchpad
> > maps the BTN_RIGHT bit, libinput assumes it is NOT a buttonpad.
> >
> > However, this change leaded to several false possitives, so we ended up
> > reverting it. For more context:
> > https://gitlab.freedesktop.org/libinput/libinput/-/issues/704
> >
> > And for a full list of affected hardware, HID reports and bug reports
> > please see:
> > https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/726
> >
> > My understanding is that buttonpads should not map BTN_RIGHT and/or
> > BTN_MIDDLE and to avoid it I would like to fix the required drivers.
> 
> As long as udev intrinsic is happy with it (and it correctly tags the
> touchpad as ID_INPUT_something), I'm fine with it.

fwiw, udev's builtin input-id touchpad check is
  ABS_X && ABS_Y && BTN_TOOL_FINGER && !BTN_TOOL_PEN && !INPUT_PROP_DIRECT
it doesn't care about the actual buttons so this patch wouldn't affect it.

> Also, you might want to point at the specification regarding button
> pads: https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/touchpad-windows-precision-touchpad-collection#device-capabilities-feature-report
> 
> The way I read it: if the device exports the Button type value
> feature, and it is 0 or 1 (click-pad or pressure-pad), there should
> not be discrete buttons.

Yeah, it sounds like there *should* not be any buttons but 
There is nothing to explicitly forbid extra buttons for click/pressurepads
which is probably how those devices get past the windows driver
implementation.

Cheers,
   Peter