touchpad: only reduce the slot count for ALPS serial touchpads

We're getting too many regressions on other devices for this feature and only
ALPS touchpads need it (it's a kernel driver bug). So let's limit this to
those devices only.

For example, synaptics serial touchpads don't keep the fake fingers and slot
states in sync when going from two to three fingers, causing an erroneous slot
downgrade. See
https://gitlab.freedesktop.org/libinput/libinput/issues/434#note_419912
That interferes with this code but fixing it is hard and anyway,
synaptics touchpads don't need the slot count drop.

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

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 998802991a7d6e1b559ce54478904997c33cebd8..c3da8f9dd5ecac658e89703b96cb5ae4b8c89ea2 100644 (file)
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -645,12 +645,14 @@ tp_process_fake_touches(struct tp_dispatch *tp,
            EVDEV_MODEL_SYNAPTICS_SERIAL_TOUCHPAD)
                tp_restore_synaptics_touches(tp, time);
 
-       /* ALPS touchpads always set 3 slots in the kernel, even
+       /* ALPS serial touchpads always set 3 slots in the kernel, even
         * where they support less than that. So we get BTN_TOOL_TRIPLETAP
         * but never slot 2 because our slot count is wrong.
         * This also means that the third touch falls through the cracks and
         * is ignored.
         *
+        * See https://gitlab.freedesktop.org/libinput/libinput/issues/408
+        *
         * All touchpad devices have at least one slot so we only do this
         * for 2 touches or higher.
         *
@@ -665,7 +667,8 @@ tp_process_fake_touches(struct tp_dispatch *tp,
         * For a long explanation of what happens, see
         * https://gitlab.freedesktop.org/libevdev/libevdev/merge_requests/19
         */
-       if (nfake_touches > 1 && tp->has_mt &&
+       if (tp->device->model_flags & EVDEV_MODEL_ALPS_SERIAL_TOUCHPAD &&
+           nfake_touches > 1 && tp->has_mt &&
            tp->nactive_slots > 0 &&
            nfake_touches > tp->nactive_slots &&
            tp->nactive_slots < tp->num_slots) {

diff --git a/src/evdev.c b/src/evdev.c
index bf85aa24dbd5d6b50dd56b08891296f57cfb041f..3f4e6aac1672c5f75d863cc0558cfe84ae1069ea 100644 (file)
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -1384,6 +1384,7 @@ evdev_read_model_flags(struct evdev_device *device)
 #define MODEL(name) { QUIRK_MODEL_##name, EVDEV_MODEL_##name }
                MODEL(WACOM_TOUCHPAD),
                MODEL(SYNAPTICS_SERIAL_TOUCHPAD),
+               MODEL(ALPS_SERIAL_TOUCHPAD),
                MODEL(LENOVO_T450_TOUCHPAD),
                MODEL(TRACKBALL),
                MODEL(APPLE_TOUCHPAD_ONEBUTTON),

diff --git a/src/evdev.h b/src/evdev.h
index e95f7e60f1dedeab919311e0ac80042bd7896bbb..0eda22f999a20f063747e6fde0f1e1a215399a45 100644 (file)
--- a/src/evdev.h
+++ b/src/evdev.h
@@ -108,6 +108,7 @@ enum evdev_device_model {
        EVDEV_MODEL_DEFAULT = 0,
        EVDEV_MODEL_WACOM_TOUCHPAD              = bit(1),
        EVDEV_MODEL_SYNAPTICS_SERIAL_TOUCHPAD   = bit(2),
+       EVDEV_MODEL_ALPS_SERIAL_TOUCHPAD        = bit(3),
        EVDEV_MODEL_LENOVO_T450_TOUCHPAD        = bit(4),
        EVDEV_MODEL_APPLE_TOUCHPAD_ONEBUTTON    = bit(5),
        EVDEV_MODEL_LENOVO_SCROLLPOINT          = bit(6),