linux-kernel - Re: [PATCH v2] Documentation: input: expand INPUT_PROP_HAPTIC

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Message-ID: <20251105060333.GA2615904@quokka>
Date: Wed, 5 Nov 2025 16:03:33 +1000
From: Peter Hutterer <peter.hutterer@...-t.net>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Jonathan Denose <jdenose@...gle.com>, Jiri Kosina <jikos@...nel.org>,
	Benjamin Tissoires <bentiss@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Henrik Rydberg <rydberg@...math.org>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Angela Czubak <aczubak@...gle.com>,
	Sean O'Brien <seobrien@...gle.com>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2] Documentation: input: expand
 INPUT_PROP_HAPTIC_TOUCHPAD to all pressure pads

On Tue, Nov 04, 2025 at 09:09:09PM -0800, Dmitry Torokhov wrote:
> Hi Peter,
> 
> On Fri, Oct 31, 2025 at 02:12:45PM +1000, Peter Hutterer wrote:
> > Definition: "pressure pad" used here as all touchpads that use physical
> > pressure to convert to click without physical hinges. Also called haptic
> > touchpads in general parlance, Synaptics calls them ForcePads.
> > 
> > Most (all?) pressure pads are currently advertised as
> > INPUT_PROP_BUTTONPAD. The suggestion to identify them as pressure pads
> > by defining the resolution on ABS_MT_PRESSURE has been in the docs since
> > commit 20ccc8dd38a3 ("Documentation: input: define
> > ABS_PRESSURE/ABS_MT_PRESSURE resolution as grams") but few devices
> > provide this information.
> > 
> > In userspace it's thus impossible to determine whether a device is a
> > true pressure pad (pressure equals pressure) or a normal clickpad with
> > (pressure equals finger size).
> > 
> > Commit 7075ae4ac9db ("Input: add INPUT_PROP_HAPTIC_TOUCHPAD") introduces
> > INPUT_PROP_HAPTIC_TOUCHPAD but restricted it to those touchpads that
> > have support for userspace-controlled effects. Let's expand that
> > definition to include all haptic touchpads (pressure pads) since those
> > that do support FF effects can be identified by the presence of the
> > FF_HAPTIC bit.
> > 
> > This means:
> > - clickpad: INPUT_PROP_BUTTONPAD
> > - pressurepad: INPUT_PROP_BUTTONPAD + INPUT_PROP_HAPTIC_TOUCHPAD
> > - pressurepad with haptics:
> >   INPUT_PROP_BUTTONPAD + INPUT_PROP_HAPTIC_TOUCHPAD + FF_HAPTIC
> 
> Should we maybe rename it to INPUT_PROP_PRESSURE_TOUCHPAD? We are within
> a release of introducing it, so we should be able to rename it without
> much fallout.

I'd be happy with a rename too. Want me to send a patch for that or do
you want to rename it locally during applying?

Cheers,
  Peter