tablet: always enable touch arbitration with touchscreens/ext. touchpads

Right now for touch arbitration to work, we require the device group to
be the same (i.e. they're hanging off the same physical bus). That's not
always the case and statistically we have a lot more devices that have
a built-in tablet + touchscreen than we have Intuos-like external
tablets.

So let's default to the more common case - enabling arbitration with the
first touchscreen/external touchpad we find. If a subsequent device is
"better", swap it out. Right now, the only heuristic we have here is the
device group check but in the future we could get more precise.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

2 files changed, 67 insertions, 14 deletions

diff --git a/src/evdev-tablet.c b/src/evdev-tablet.c
index 4bc12632..c8d7ebb5 100644
--- a/src/evdev-tablet.c
+++ b/src/evdev-tablet.c
@@ -2150,6 +2150,30 @@ tablet_setup_touch_arbitration(struct evdev_device *device,
 {
 	struct tablet_dispatch *tablet = tablet_dispatch(device->dispatch);
 
+        /* We enable touch arbitration with the first touch screen/external
+         * touchpad we see. This may be wrong in some cases, so we have some
+         * heuristics in case we find a "better" device.
+         */
+        if (tablet->touch_device != NULL) {
+		struct libinput_device_group *group1 = libinput_device_get_device_group(&device->base);
+		struct libinput_device_group *group2 = libinput_device_get_device_group(&new_device->base);
+
+		/* same phsical device? -> better, otherwise keep the one we have */
+		if (group1 != group2)
+			return;
+
+		/* We found a better device, let's swap it out */
+		struct libinput *li = tablet_libinput_context(tablet);
+		tablet_set_touch_device_enabled(tablet,
+						ARBITRATION_NOT_ACTIVE,
+						NULL,
+						libinput_now(li));
+		evdev_log_debug(device,
+				"touch-arbitration: removing pairing for %s<->%s\n",
+				device->devname,
+				tablet->touch_device->devname);
+	}
+
 	evdev_log_debug(device,
 			"touch-arbitration: activated for %s<->%s\n",
 			device->devname,
@@ -2162,16 +2186,20 @@ tablet_setup_rotation(struct evdev_device *device,
 		      struct evdev_device *new_device)
 {
 	struct tablet_dispatch *tablet = tablet_dispatch(device->dispatch);
-
-	evdev_log_debug(device,
-			"tablet-rotation: %s will rotate %s\n",
-			device->devname,
-			new_device->devname);
-	tablet->rotation.touch_device = new_device;
-
-	if (libinput_device_config_left_handed_get(&new_device->base)) {
-		tablet->rotation.touch_device_left_handed_state = true;
-		tablet_change_rotation(device, DO_NOTIFY);
+	struct libinput_device_group *group1 = libinput_device_get_device_group(&device->base);
+	struct libinput_device_group *group2 = libinput_device_get_device_group(&new_device->base);
+
+	if (tablet->rotation.touch_device == NULL && (group1 == group2)) {
+		evdev_log_debug(device,
+				"tablet-rotation: %s will rotate %s\n",
+				device->devname,
+				new_device->devname);
+		tablet->rotation.touch_device = new_device;
+
+		if (libinput_device_config_left_handed_get(&new_device->base)) {
+			tablet->rotation.touch_device_left_handed_state = true;
+			tablet_change_rotation(device, DO_NOTIFY);
+		}
 	}
 }
 
@@ -2181,10 +2209,6 @@ tablet_device_added(struct evdev_device *device,
 {
 	bool is_touchscreen, is_ext_touchpad;
 
-	if (libinput_device_get_device_group(&device->base) !=
-	    libinput_device_get_device_group(&added_device->base))
-		return;
-
 	is_touchscreen = evdev_device_has_capability(added_device,
 						     LIBINPUT_DEVICE_CAP_TOUCH);
 	is_ext_touchpad = evdev_device_has_capability(added_device,
diff --git a/test/test-tablet.c b/test/test-tablet.c
index 5a92ea6e..9a6602e6 100644
--- a/test/test-tablet.c
+++ b/test/test-tablet.c
@@ -5338,6 +5338,34 @@ START_TEST(touch_arbitration_late_touch_lift)
 }
 END_TEST
 
+START_TEST(touch_arbitration_swap_device)
+{
+	struct litest_device *tablet = litest_current_device();
+	struct libinput *li = tablet->libinput;
+
+	enum litest_device_type paired = paired_device(tablet);
+	if (paired == LITEST_NO_DEVICE)
+		return;
+
+	/* First, add a normal touchscreen */
+	struct litest_device *touchscreen = litest_add_device(li, LITEST_GENERIC_MULTITOUCH_SCREEN);
+	libinput_device_config_gesture_set_hold_enabled(touchscreen->libinput_device,
+							LIBINPUT_CONFIG_HOLD_DISABLED);
+	litest_drain_events(li);
+	assert_touch_is_arbitrated(tablet, touchscreen);
+
+	/* Now add a better device to override the pairing */
+	struct litest_device *finger = litest_add_device(li, paired);
+	libinput_device_config_gesture_set_hold_enabled(finger->libinput_device,
+							LIBINPUT_CONFIG_HOLD_DISABLED);
+	litest_drain_events(li);
+	assert_touch_is_arbitrated(tablet, finger);
+
+	litest_delete_device(touchscreen);
+	litest_delete_device(finger);
+}
+END_TEST
+
 #if HAVE_LIBWACOM
 static void
 verify_left_handed_tablet_motion(struct litest_device *tablet,
@@ -6209,6 +6237,7 @@ TEST_COLLECTION(tablet)
 	litest_add(touch_arbitration_late_touch_lift, LITEST_TABLET, LITEST_ANY);
 	litest_add(touch_arbitration_outside_rect, LITEST_TABLET | LITEST_DIRECT, LITEST_ANY);
 	litest_add(touch_arbitration_remove_after, LITEST_TABLET | LITEST_DIRECT, LITEST_ANY);
+	litest_add(touch_arbitration_swap_device, LITEST_TABLET, LITEST_ANY);
 
 	litest_add_ranged(tablet_rotation_left_handed, LITEST_TABLET, LITEST_ANY, &lh_transitions);
 	litest_add_ranged(tablet_rotation_left_handed_configuration, LITEST_TABLET, LITEST_ANY, &lh_transitions);