Input: rename INPUT_PROP_HAPTIC_TOUCHPAD to INPUT_PROP_PRESSUREPAD

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 20ccc8d ("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 7075ae4 ("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@who-t.net>
Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://patch.msgid.link/20251106114534.GA405512@tassie
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: whot

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
 ==========

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;

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)