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Message-ID: <c7popmowkdilnthufvne4rednntgae2cxqwdvmd3tkfeji24nl@yhpwili7qobt>
Date: Thu, 6 Nov 2025 15:32:56 +0100
From: Benjamin Tissoires <bentiss@...nel.org>
To: Peter Hutterer <peter.hutterer@...-t.net>
Cc: 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
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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