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Message-ID: <20251113092016.GA1843303@quokka>
Date: Thu, 13 Nov 2025 19:20:16 +1000
From: Peter Hutterer <peter.hutterer@...-t.net>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Benjamin Tissoires <bentiss@...nel.org>,
Jonathan Denose <jdenose@...gle.com>,
Jiri Kosina <jikos@...nel.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
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 v3] Input: rename INPUT_PROP_HAPTIC_TOUCHPAD to
INPUT_PROP_PRESSUREPAD
Dmitry - gentle ping?
Cheers,
Peter
On Thu, Nov 06, 2025 at 03:32:56PM +0100, Benjamin Tissoires wrote:
> On Nov 06 2025, Peter Hutterer wrote:
> > And expand it to encompass all pressure pads.
> >
> > Definition: "pressure pad" as used here as includes 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 and rename
> > that definition to include all pressure pad touchpads 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_PRESSUREPAD
> > - pressurepad with configurable haptics:
> > INPUT_PROP_BUTTONPAD + INPUT_PROP_PRESSUREPAD + FF_HAPTIC
> >
> > Signed-off-by: Peter Hutterer <peter.hutterer@...-t.net>
>
> Acked-by: Benjamin Tissoires <bentiss@...nel.org>
>
> Unless Jiri has any problem with it, I guess this would be fine going
> through your tree Dmitry.
>
> Cheers,
> Benjamin
>
>
> > ---
> > ftr, I picked PRESSUREPAD over Dmitry's PRESSURE_TOUCHPAD suggestion
> > because it matches better with the existing BUTTONPAD.
> >
> > Changes to v1: extra empty lines to render the lists as lists
> > Changes to v2: rename to PRESSUREPAD and rename it in the instances
> > where it's used in the code
> >
> > v1: https://lore.kernel.org/linux-input/20251030011735.GA969565@quokka/T/#u
> > v2: https://lore.kernel.org/linux-input/20251030011735.GA969565@quokka/T/#m9504de27b02d00a55d540fd9fec9aed3edd0133c
> >
> > Documentation/input/event-codes.rst | 25 ++++++++++++++++++-------
> > drivers/hid/hid-haptic.c | 2 +-
> > include/uapi/linux/input-event-codes.h | 2 +-
> > 3 files changed, 20 insertions(+), 9 deletions(-)
> >
> > diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
> > index 1ead9bb8d9c6..4424cbff251f 100644
> > --- a/Documentation/input/event-codes.rst
> > +++ b/Documentation/input/event-codes.rst
> > @@ -400,19 +400,30 @@ can report through the rotational axes (absolute and/or relative rx, ry, rz).
> > All other axes retain their meaning. A device must not mix
> > regular directional axes and accelerometer axes on the same event node.
> >
> > -INPUT_PROP_HAPTIC_TOUCHPAD
> > ---------------------------
> > +INPUT_PROP_PRESSUREPAD
> > +----------------------
> > +
> > +The INPUT_PROP_PRESSUREPAD property indicates that the device provides
> > +simulated haptic feedback (e.g. a vibrator motor situated below the surface)
> > +instead of physical haptic feedback (e.g. a hinge). This property is only set
> > +if the device:
> >
> > -The INPUT_PROP_HAPTIC_TOUCHPAD property indicates that device:
> > -- supports simple haptic auto and manual triggering
> > - can differentiate between at least 5 fingers
> > - uses correct resolution for the X/Y (units and value)
> > -- reports correct force per touch, and correct units for them (newtons or grams)
> > - follows the MT protocol type B
> >
> > +If the simulated haptic feedback is controllable by userspace the device must:
> > +
> > +- support simple haptic auto and manual triggering, and
> > +- report correct force per touch, and correct units for them (newtons or grams), and
> > +- provide the EV_FF FF_HAPTIC force feedback effect.
> > +
> > Summing up, such devices follow the MS spec for input devices in
> > -Win8 and Win8.1, and in addition support the Simple haptic controller HID table,
> > -and report correct units for the pressure.
> > +Win8 and Win8.1, and in addition may support the Simple haptic controller HID
> > +table, and report correct units for the pressure.
> > +
> > +Where applicable, this property is set in addition to INPUT_PROP_BUTTONPAD, it
> > +does not replace that property.
> >
> > Guidelines
> > ==========
> > diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
> > index aa090684c1f2..fc8a9997f815 100644
> > --- a/drivers/hid/hid-haptic.c
> > +++ b/drivers/hid/hid-haptic.c
> > @@ -86,7 +86,7 @@ int hid_haptic_input_configured(struct hid_device *hdev,
> > if (hi->application == HID_DG_TOUCHPAD) {
> > if (haptic->auto_trigger_report &&
> > haptic->manual_trigger_report) {
> > - __set_bit(INPUT_PROP_HAPTIC_TOUCHPAD, hi->input->propbit);
> > + __set_bit(INPUT_PROP_PRESSUREPAD, hi->input->propbit);
> > return 1;
> > }
> > return 0;
> > diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
> > index 8ba48590bd2c..d21172c6a266 100644
> > --- a/include/uapi/linux/input-event-codes.h
> > +++ b/include/uapi/linux/input-event-codes.h
> > @@ -27,7 +27,7 @@
> > #define INPUT_PROP_TOPBUTTONPAD 0x04 /* softbuttons at top of pad */
> > #define INPUT_PROP_POINTING_STICK 0x05 /* is a pointing stick */
> > #define INPUT_PROP_ACCELEROMETER 0x06 /* has accelerometer */
> > -#define INPUT_PROP_HAPTIC_TOUCHPAD 0x07 /* is a haptic touchpad */
> > +#define INPUT_PROP_PRESSUREPAD 0x07 /* pressure triggers clicks */
> >
> > #define INPUT_PROP_MAX 0x1f
> > #define INPUT_PROP_CNT (INPUT_PROP_MAX + 1)
> > --
> > 2.51.1
> >
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