touchpad: add quirk for the T450 and T460 generation hardware

The touchpad's sensors are too far apart (or the firmware interferes), causing
in a jerky movement visible especially on slow motion. We get a bunch of
normal motion events, then only ABS_MT_PRESSURE updates without x/y updates.
After about one mm of movement x/y updates resume, with the first event
covering the distance between the last motion event. That event is usually
accelerated and thus causes a large jump. Subsequent events are sufficiently
fine-grained again.

This patch counts the number of non-motion events. Once we hit 10 in a row, we
mark the first motion update as non-dirty, effectively discarding the motion
and thus stopping the pointer jumps.

https://bugs.freedesktop.org/show_bug.cgi?id=94379

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

src/evdev-mt-touchpad.c

@@ -337,7 +337,7 @@ tp_process_absolute(struct tp_dispatch *tp,
 	case ABS_MT_PRESSURE:
 		t->pressure = e->value;
 		t->dirty = true;
-		tp->queued |= TOUCHPAD_EVENT_MOTION;
+		tp->queued |= TOUCHPAD_EVENT_OTHERAXIS;
 		break;
 	}
 }
@@ -880,8 +880,10 @@ tp_position_fake_touches(struct tp_dispatch *tp)
 }
 
 static inline bool
-tp_need_motion_history_reset(struct tp_dispatch *tp)
+tp_need_motion_history_reset(struct tp_dispatch *tp, uint64_t time)
 {
+	bool rc = false;
+
 	/* semi-mt finger postions may "jump" when nfingers changes */
 	if (tp->semi_mt && tp->nfingers_down != tp->old_nfingers_down)
 		return true;
@@ -894,7 +896,29 @@ tp_need_motion_history_reset(struct tp_dispatch *tp)
 		 tp->old_nfingers_down > tp->num_slots))
 		return true;
 
-	return false;
+	/* Quirk: if we had multiple events without x/y axis
+	   information, the next x/y event is going to be a jump. So we
+	   reset that touch to non-dirty effectively swallowing that event
+	   and restarting with the next event again.
+	 */
+	if (tp->device->model_flags & EVDEV_MODEL_LENOVO_T450_TOUCHPAD) {
+		if (tp->queued & TOUCHPAD_EVENT_MOTION) {
+			if (tp->quirks.nonmotion_event_count > 10) {
+				struct tp_touch *t;
+
+				tp_for_each_touch(tp, t)
+				t->dirty = false;
+				rc = true;
+			}
+			tp->quirks.nonmotion_event_count = 0;
+		}
+
+		if ((tp->queued & (TOUCHPAD_EVENT_OTHERAXIS|TOUCHPAD_EVENT_MOTION)) ==
+		    TOUCHPAD_EVENT_OTHERAXIS)
+			tp->quirks.nonmotion_event_count++;
+	}
+
+	return rc;
 }
 
 static void
@@ -909,7 +933,7 @@ tp_process_state(struct tp_dispatch *tp, uint64_t time)
 	tp_unhover_touches(tp, time);
 	tp_position_fake_touches(tp);
 
-	want_motion_reset = tp_need_motion_history_reset(tp);
+	want_motion_reset = tp_need_motion_history_reset(tp, time);
 
 	for (i = 0; i < tp->ntouches; i++) {
 		t = tp_get_touch(tp, i);

src/evdev-mt-touchpad.h

@@ -41,6 +41,7 @@ enum touchpad_event {
 	TOUCHPAD_EVENT_MOTION		= (1 << 0),
 	TOUCHPAD_EVENT_BUTTON_PRESS	= (1 << 1),
 	TOUCHPAD_EVENT_BUTTON_RELEASE	= (1 << 2),
+	TOUCHPAD_EVENT_OTHERAXIS	= (1 << 3),
 };
 
 enum touchpad_model {
@@ -353,6 +354,17 @@ struct tp_dispatch {
 		int upper_thumb_line;
 		int lower_thumb_line;
 	} thumb;
+
+	struct {
+		/* A quirk used on the T450 series Synaptics hardware.
+		 * Slowly moving the finger causes multiple events with only
+		 * ABS_MT_PRESSURE but no x/y information. When the x/y
+		 * event comes, it will be a jump of ~20 units. We use the
+		 * below to count non-motion events to discard that first
+		 * event with the jump.
+		 */
+		unsigned int nonmotion_event_count;
+	} quirks;
 };
 
 #define tp_for_each_touch(_tp, _t) \

src/evdev.c

@@ -1680,6 +1680,7 @@ evdev_read_model_flags(struct evdev_device *device)
 		{ "LIBINPUT_MODEL_CYBORG_RAT", EVDEV_MODEL_CYBORG_RAT },
 		{ "LIBINPUT_MODEL_CYAPA", EVDEV_MODEL_CYAPA },
 		{ "LIBINPUT_MODEL_ALPS_RUSHMORE", EVDEV_MODEL_ALPS_RUSHMORE },
+		{ "LIBINPUT_MODEL_LENOVO_T450_TOUCHPAD", EVDEV_MODEL_LENOVO_T450_TOUCHPAD },
 		{ NULL, EVDEV_MODEL_DEFAULT },
 	};
 	const struct model_map *m = model_map;

src/evdev.h

@@ -113,6 +113,7 @@ enum evdev_device_model {
 	EVDEV_MODEL_CYBORG_RAT = (1 << 14),
 	EVDEV_MODEL_CYAPA = (1 << 15),
 	EVDEV_MODEL_ALPS_RUSHMORE = (1 << 16),
+	EVDEV_MODEL_LENOVO_T450_TOUCHPAD= (1 << 17),
 };
 
 struct mt_slot {

udev/90-libinput-model-quirks.hwdb

@@ -100,6 +100,13 @@ libinput:name:Cypress APA Trackpad (cyapa):dmi:*
 libinput:name:SynPS/2 Synaptics TouchPad:dmi:*svnLENOVO:*:pvrThinkPadX230*
  LIBINPUT_MODEL_LENOVO_X230=1
 
+# Lenovo T450/T460 and all other Lenovos of the *50 and *60 generation,
+# including the X1 Carbon 3rd gen
+libinput:name:SynPS/2 Synaptics TouchPad:dmi:*svnLENOVO:*:pvrThinkPad??50*:
+libinput:name:SynPS/2 Synaptics TouchPad:dmi:*svnLENOVO:*:pvrThinkPad??60*:
+libinput:name:SynPS/2 Synaptics TouchPad:dmi:*svnLENOVO:*:pvrThinkPadX1Carbon3rd:*
+ LIBINPUT_MODEL_LENOVO_T450_TOUCHPAD=1
+
 ##########################################
 # Synaptics
 ##########################################