touchpad: disable MT for all semi-mt devices

Synaptics, Elantech and Alps semi-mt devices all have issues with reporting
correct MT data, even the bounding box which semi-mt devices are supposed to
report is wrong.

Synaptics devices have massive jumps with two fingers down. Elantech devices
may open slots without coordinate data. Alps devices may send 0/0 coordinates
as initial slot position.

All these may be addressable with specific quirks, but the actual benefit is
largely restricted to better palm detection (though even with quirks this is
unlikely to work) and support for pinch gestures (again, lack of coordinates
makes supporting those hard anyway).

Elantech: https://bugs.freedesktop.org/show_bug.cgi?id=93583
Alps: https://bugzilla.redhat.com/show_bug.cgi?id=1295073

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

2 files changed, 24 insertions, 40 deletions

diff --git a/src/evdev-mt-touchpad-gestures.c b/src/evdev-mt-touchpad-gestures.c
index 80aa89ff..53a71495 100644
--- a/src/evdev-mt-touchpad-gestures.c
+++ b/src/evdev-mt-touchpad-gestures.c
@@ -184,18 +184,7 @@ tp_gesture_get_direction(struct tp_dispatch *tp, struct tp_touch *touch)
 {
 	struct normalized_coords normalized;
 	struct device_float_coords delta;
-	double move_threshold;
-
-	/*
-	 * Semi-mt touchpads have somewhat inaccurate coordinates when
-	 * 2 fingers are down, so use a slightly larger threshold.
-	 * Elantech semi-mt touchpads are accurate enough though.
-	 */
-	if (tp->semi_mt &&
-	    (tp->device->model_flags & EVDEV_MODEL_ELANTECH_TOUCHPAD) == 0)
-		move_threshold = TP_MM_TO_DPI_NORMALIZED(4);
-	else
-		move_threshold = TP_MM_TO_DPI_NORMALIZED(1);
+	double move_threshold = TP_MM_TO_DPI_NORMALIZED(1);
 
 	delta = device_delta(touch->point, touch->gesture.initial);
 
@@ -221,11 +210,7 @@ tp_gesture_get_pinch_info(struct tp_dispatch *tp,
 	delta = device_delta(first->point, second->point);
 	normalized = tp_normalize_delta(tp, delta);
 	*distance = normalized_length(normalized);
-
-	if (!tp->semi_mt)
-		*angle = atan2(normalized.y, normalized.x) * 180.0 / M_PI;
-	else
-		*angle = 0.0;
+	*angle = atan2(normalized.y, normalized.x) * 180.0 / M_PI;
 
 	*center = device_average(first->point, second->point);
 }
@@ -260,6 +245,9 @@ tp_gesture_twofinger_handle_state_none(struct tp_dispatch *tp, uint64_t time)
 	first->gesture.initial = first->point;
 	second->gesture.initial = second->point;
 
+	if (!tp->gesture.enabled)
+		return GESTURE_2FG_STATE_SCROLL;
+
 	return GESTURE_2FG_STATE_UNKNOWN;
 }
 
@@ -297,7 +285,7 @@ tp_gesture_twofinger_handle_state_unknown(struct tp_dispatch *tp, uint64_t time)
 	    ((dir2 & 0x80) && (dir1 & 0x01))) {
 		tp_gesture_set_scroll_buildup(tp);
 		return GESTURE_2FG_STATE_SCROLL;
-	} else if (tp->gesture.enabled) {
+	} else {
 		tp_gesture_get_pinch_info(tp,
 					  &tp->gesture.initial_distance,
 					  &tp->gesture.angle,
@@ -317,16 +305,7 @@ tp_gesture_twofinger_handle_state_scroll(struct tp_dispatch *tp, uint64_t time)
 	if (tp->scroll.method != LIBINPUT_CONFIG_SCROLL_2FG)
 		return GESTURE_2FG_STATE_SCROLL;
 
-	/* On some semi-mt models slot 0 is more accurate, so for semi-mt
-	 * we only use slot 0. */
-	if (tp->semi_mt) {
-		if (!tp->touches[0].dirty)
-			return GESTURE_2FG_STATE_SCROLL;
-
-		delta = tp_get_delta(&tp->touches[0]);
-	} else {
-		delta = tp_get_average_touches_delta(tp);
-	}
+	delta = tp_get_average_touches_delta(tp);
 
 	/* scroll is not accelerated */
 	delta = tp_filter_motion_unaccelerated(tp, &delta, time);
@@ -568,10 +547,10 @@ tp_gesture_handle_state(struct tp_dispatch *tp, uint64_t time)
 int
 tp_init_gesture(struct tp_dispatch *tp)
 {
-	if (tp->device->model_flags & EVDEV_MODEL_JUMPING_SEMI_MT)
-		tp->gesture.enabled = false;
-	else
-		tp->gesture.enabled = true;
+	/* two-finger scrolling is always enabled, this flag just
+	 * decides whether we detect pinch. semi-mt devices are too
+	 * unreliable to do pinch gestures. */
+	tp->gesture.enabled = !tp->semi_mt;
 
 	tp->gesture.twofinger_state = GESTURE_2FG_STATE_NONE;
 
diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 62087fb0..7f5bbf53 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -1490,17 +1490,22 @@ tp_init_slots(struct tp_dispatch *tp,
 
 	tp->semi_mt = libevdev_has_property(device->evdev, INPUT_PROP_SEMI_MT);
 
-	/* This device has a terrible resolution when two fingers are down,
+	/* Semi-mt devices are not reliable for true multitouch data, so we
+	 * simply pretend they're single touch touchpads with BTN_TOOL bits.
+	 * Synaptics:
+	 * Terrible resolution when two fingers are down,
 	 * causing scroll jumps. The single-touch emulation ABS_X/Y is
 	 * accurate but the ABS_MT_POSITION touchpoints report the bounding
-	 * box and that causes jumps.  So we simply pretend it's a single
-	 * touch touchpad with the BTN_TOOL bits.
-	 * See https://bugzilla.redhat.com/show_bug.cgi?id=1235175 for an
-	 * explanation.
+	 * box and that causes jumps. See https://bugzilla.redhat.com/1235175
+	 * Elantech:
+	 * On three-finger taps/clicks, one slot doesn't get a coordinate
+	 * assigned. See https://bugs.freedesktop.org/show_bug.cgi?id=93583
+	 * Alps:
+	 * If three fingers are set down in the same frame, one slot has the
+	 * coordinates 0/0 and may not get updated for several frames.
+	 * See https://bugzilla.redhat.com/show_bug.cgi?id=1295073
 	 */
-	if (tp->semi_mt &&
-	    (device->model_flags &
-	     (EVDEV_MODEL_JUMPING_SEMI_MT|EVDEV_MODEL_ELANTECH_TOUCHPAD))) {
+	if (tp->semi_mt) {
 		tp->num_slots = 1;
 		tp->slot = 0;
 		tp->has_mt = false;