[PATCH v2 libinput] touchpad: drop motion hysteresis by default

[Peter Hutterer]

Some older touchpad devices jitter a fair bit when a finger is resting on the
touchpad. That's why the hysteresis was introduced in the synaptics driver
back in 2011. However, the default value of the hysteresis in the synaptics
driver ended up being 0, even though the code looks like it's using a fraction
of the touchpad diagonal. When the hysteresis code was ported to libinput it
was eventually set to 0.5mm.

Turns out this is still too high and tiny finger motions are either
nonreactive or quite jumpy, making it hard to select small targets. Drop the
default hysteresis by reducing its margin to 0, but leave it in place for
those devices where we need them (e.g. the cyapa touchpads).

https://bugs.freedesktop.org/show_bug.cgi?id=93503

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
Changes to v1:
- add exception for the cyapa touchpads

I'm purposely only including that one model because we know that it needs
the hysteresis. Over time, there will be other devices that need it, but
let's fix those up as we find them rather than erring on the side of
including a bunch of devices that may not need it, the improvements to slow
motion are too good to ignore

 src/evdev-mt-touchpad.c            | 23 ++++++++++++++++++-----
 src/evdev.c                        |  1 +
 src/evdev.h                        |  1 +
 udev/90-libinput-model-quirks.hwdb |  3 +++
 4 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index f249116..0f72807 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -1951,13 +1951,29 @@ tp_init_default_resolution(struct tp_dispatch *tp,
 	return 0;
 }
 
+static inline void
+tp_init_hysteresis(struct tp_dispatch *tp)
+{
+	int res_x, res_y;
+
+	res_x = tp->device->abs.absinfo_x->resolution;
+	res_y = tp->device->abs.absinfo_y->resolution;
+
+	if (tp->device->model_flags & EVDEV_MODEL_CYAPA) {
+		tp->hysteresis_margin.x = res_x/2;
+		tp->hysteresis_margin.y = res_y/2;
+	} else {
+		tp->hysteresis_margin.x = 0;
+		tp->hysteresis_margin.y = 0;
+	}
+}
+
 static int
 tp_init(struct tp_dispatch *tp,
 	struct evdev_device *device)
 {
 	int width, height;
 	double diagonal;
-	int res_x, res_y;
 
 	tp->base.interface = &tp_interface;
 	tp->device = device;
@@ -1971,8 +1987,6 @@ tp_init(struct tp_dispatch *tp,
 	if (tp_init_slots(tp, device) != 0)
 		return -1;
 
-	res_x = tp->device->abs.absinfo_x->resolution;
-	res_y = tp->device->abs.absinfo_y->resolution;
 	width = device->abs.dimensions.x;
 	height = device->abs.dimensions.y;
 	diagonal = sqrt(width*width + height*height);
@@ -1981,8 +1995,7 @@ tp_init(struct tp_dispatch *tp,
 						       EV_ABS,
 						       ABS_MT_DISTANCE);
 
-	tp->hysteresis_margin.x = res_x/2;
-	tp->hysteresis_margin.y = res_y/2;
+	tp_init_hysteresis(tp);
 
 	if (tp_init_accel(tp, diagonal) != 0)
 		return -1;
diff --git a/src/evdev.c b/src/evdev.c
index 66673a8..473ff63 100644
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -1678,6 +1678,7 @@ evdev_read_model_flags(struct evdev_device *device)
 		{ "LIBINPUT_MODEL_ELANTECH_TOUCHPAD", EVDEV_MODEL_ELANTECH_TOUCHPAD },
 		{ "LIBINPUT_MODEL_APPLE_INTERNAL_KEYBOARD", EVDEV_MODEL_APPLE_INTERNAL_KEYBOARD },
 		{ "LIBINPUT_MODEL_CYBORG_RAT", EVDEV_MODEL_CYBORG_RAT },
+		{ "LIBINPUT_MODEL_CYAPA", EVDEV_MODEL_CYAPA },
 		{ NULL, EVDEV_MODEL_DEFAULT },
 	};
 	const struct model_map *m = model_map;
diff --git a/src/evdev.h b/src/evdev.h
index 8b567a8..b164af8 100644
--- a/src/evdev.h
+++ b/src/evdev.h
@@ -111,6 +111,7 @@ enum evdev_device_model {
 	EVDEV_MODEL_LENOVO_X220_TOUCHPAD_FW81 = (1 << 12),
 	EVDEV_MODEL_APPLE_INTERNAL_KEYBOARD = (1 << 13),
 	EVDEV_MODEL_CYBORG_RAT = (1 << 14),
+	EVDEV_MODEL_CYAPA = (1 << 15),
 };
 
 struct mt_slot {
diff --git a/udev/90-libinput-model-quirks.hwdb b/udev/90-libinput-model-quirks.hwdb
index fa668d6..f23a7f9 100644
--- a/udev/90-libinput-model-quirks.hwdb
+++ b/udev/90-libinput-model-quirks.hwdb
@@ -73,6 +73,9 @@ libinput:name:Cypress APA Trackpad (cyapa):dmi:*svn*SAMSUNG*:pn*Lumpy*
 libinput:name:Atmel maXTouch Touchpad:dmi:*svn*GOOGLE*:pn*Samus*
  LIBINPUT_MODEL_CHROMEBOOK=1
 
+libinput:name:Cypress APA Trackpad (cyapa):dmi:*
+ LIBINPUT_MODEL_CYAPA=1
+
 ##########################################
 # LENOVO
 ##########################################
-- 
2.5.0