[PATCH 0/2] HID: multitouch: fix sticky-fingers quirks

[PATCH 0/2] HID: multitouch: fix sticky-fingers quirks

[Benjamin Tissoires]

According to Peter, we've had for a very long time an issue on some
mutltiouch touchpads where the fingers were stuck in a scrolling mode,
or 3 fingers gesture mode. I was unable to debug it because it was
rather hard to reproduce.

Recently, some people raised the issue again on libinput, and this time
added a recording of the actual bug.

It turns out that the sticky finger quirk that was introduced back in
2017 was only checking the last report, and that those missing releases
also happen when moving from 3 to 1 finger (only 1 is released instead
of 2).

This solution seems to me to be the most sensible, because we could also
add the NSMU quirk to win8 multitouch touchpads, but this would involve
a lot more computations at each report for rather annoying corner cases.

Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/1194
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
Benjamin Tissoires (2):
      HID: multitouch: fix sticky fingers
      selftests/hid: add tests for missing release on the Dell Synaptics

 drivers/hid/hid-multitouch.c                       | 27 ++++++-----
 .../testing/selftests/hid/tests/test_multitouch.py | 55 ++++++++++++++++++++++
 2 files changed, 69 insertions(+), 13 deletions(-)
---
base-commit: 54ba6d9b1393a0061600c0e49c8ebef65d60a8b2
change-id: 20250926-fix-sticky-fingers-8ae88436ae82

Best regards,
-- 
Benjamin Tissoires <bentiss@kernel.org>

[PATCH 1/2] HID: multitouch: fix sticky fingers

[Benjamin Tissoires]

The sticky fingers quirk (MT_QUIRK_STICKY_FINGERS) was only considering
the case when slots were not released during the last report.
This can be problematic if the firmware forgets to release a finger
while others are still present.

This was observed on the Synaptics DLL0945 touchpad found on the Dell
XPS 9310 and the Dell Inspiron 5406.

Fixes: 4f4001bc76fd ("HID: multitouch: fix rare Win 8 cases when the touch up event gets missing")
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 drivers/hid/hid-multitouch.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 2879e65cf303b1456311ac06115adda5a78a2600..e1a5c7f3a25132094ed643910337474025852b22 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -94,9 +94,8 @@ enum report_mode {
 	TOUCHPAD_REPORT_ALL = TOUCHPAD_REPORT_BUTTONS | TOUCHPAD_REPORT_CONTACTS,
 };
 
-#define MT_IO_FLAGS_RUNNING		0
-#define MT_IO_FLAGS_ACTIVE_SLOTS	1
-#define MT_IO_FLAGS_PENDING_SLOTS	2
+#define MT_IO_SLOTS_MASK		GENMASK(7, 0) /* reserve first 8 bits for slot tracking */
+#define MT_IO_FLAGS_RUNNING		32
 
 static const bool mtrue = true;		/* default for true */
 static const bool mfalse;		/* default for false */
@@ -172,7 +171,11 @@ struct mt_device {
 	struct timer_list release_timer;	/* to release sticky fingers */
 	struct hid_haptic_device *haptic;	/* haptic related configuration */
 	struct hid_device *hdev;	/* hid_device we're attached to */
-	unsigned long mt_io_flags;	/* mt flags (MT_IO_FLAGS_*) */
+	unsigned long mt_io_flags;	/* mt flags (MT_IO_FLAGS_RUNNING)
+					 * first 8 bits are reserved for keeping the slot
+					 * states, this is fine because we only support up
+					 * to 250 slots (MT_MAX_MAXCONTACT)
+					 */
 	__u8 inputmode_value;	/* InputMode HID feature value */
 	__u8 maxcontacts;
 	bool is_buttonpad;	/* is this device a button pad? */
@@ -986,6 +989,7 @@ static void mt_release_pending_palms(struct mt_device *td,
 
 	for_each_set_bit(slotnum, app->pending_palm_slots, td->maxcontacts) {
 		clear_bit(slotnum, app->pending_palm_slots);
+		clear_bit(slotnum, &td->mt_io_flags);
 
 		input_mt_slot(input, slotnum);
 		input_mt_report_slot_inactive(input);
@@ -1019,12 +1023,6 @@ static void mt_sync_frame(struct mt_device *td, struct mt_application *app,
 	app->left_button_state = 0;
 	if (td->is_haptic_touchpad)
 		hid_haptic_pressure_reset(td->haptic);
-
-	if (test_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags))
-		set_bit(MT_IO_FLAGS_PENDING_SLOTS, &td->mt_io_flags);
-	else
-		clear_bit(MT_IO_FLAGS_PENDING_SLOTS, &td->mt_io_flags);
-	clear_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags);
 }
 
 static int mt_compute_timestamp(struct mt_application *app, __s32 value)
@@ -1202,7 +1200,9 @@ static int mt_process_slot(struct mt_device *td, struct input_dev *input,
 		input_event(input, EV_ABS, ABS_MT_TOUCH_MAJOR, major);
 		input_event(input, EV_ABS, ABS_MT_TOUCH_MINOR, minor);
 
-		set_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags);
+		set_bit(slotnum, &td->mt_io_flags);
+	} else {
+		clear_bit(slotnum, &td->mt_io_flags);
 	}
 
 	return 0;
@@ -1337,7 +1337,7 @@ static void mt_touch_report(struct hid_device *hid,
 	 * defect.
 	 */
 	if (app->quirks & MT_QUIRK_STICKY_FINGERS) {
-		if (test_bit(MT_IO_FLAGS_PENDING_SLOTS, &td->mt_io_flags))
+		if (td->mt_io_flags & MT_IO_SLOTS_MASK)
 			mod_timer(&td->release_timer,
 				  jiffies + msecs_to_jiffies(100));
 		else
@@ -1813,6 +1813,7 @@ static void mt_release_contacts(struct hid_device *hid)
 			for (i = 0; i < mt->num_slots; i++) {
 				input_mt_slot(input_dev, i);
 				input_mt_report_slot_inactive(input_dev);
+				clear_bit(i, &td->mt_io_flags);
 			}
 			input_mt_sync_frame(input_dev);
 			input_sync(input_dev);
@@ -1835,7 +1836,7 @@ static void mt_expired_timeout(struct timer_list *t)
 	 */
 	if (test_and_set_bit_lock(MT_IO_FLAGS_RUNNING, &td->mt_io_flags))
 		return;
-	if (test_bit(MT_IO_FLAGS_PENDING_SLOTS, &td->mt_io_flags))
+	if (td->mt_io_flags & MT_IO_SLOTS_MASK)
 		mt_release_contacts(hdev);
 	clear_bit_unlock(MT_IO_FLAGS_RUNNING, &td->mt_io_flags);
 }

-- 
2.51.0

[PATCH 2/2] selftests/hid: add tests for missing release on the Dell Synaptics

[Benjamin Tissoires]

Add a simple test for the corner case not currently covered by the
sticky fingers quirk. Because it's a corner case test, we only test this
on a couple of devices, not on all of them because the value of adding
the same test over and over is rather moot.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 .../testing/selftests/hid/tests/test_multitouch.py | 55 ++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/tools/testing/selftests/hid/tests/test_multitouch.py b/tools/testing/selftests/hid/tests/test_multitouch.py
index 5d2ffa3d59777e3cd93d1d7aebabc2a6b7ecb42a..ece0ba8e7d34b75d42245e5936ecf804c46b0846 100644
--- a/tools/testing/selftests/hid/tests/test_multitouch.py
+++ b/tools/testing/selftests/hid/tests/test_multitouch.py
@@ -1752,6 +1752,52 @@ class TestWin8TSConfidence(BaseTest.TestWin8Multitouch):
         assert evdev.slots[0][libevdev.EV_ABS.ABS_MT_TRACKING_ID] == -1
 
 
+    @pytest.mark.skip_if_uhdev(
+        lambda uhdev: "Confidence" not in uhdev.fields,
+        "Device not compatible, missing Confidence usage",
+    )
+    def test_mt_confidence_bad_multi_release(self):
+        """Check for the sticky finger being properly detected.
+
+        We first inject 3 fingers, then release only the second.
+        After 100 ms, we should receive a generated event about the
+        2 missing fingers being released.
+        """
+        uhdev = self.uhdev
+        evdev = uhdev.get_evdev()
+
+        # send 3 touches
+        t0 = Touch(1, 50, 10)
+        t1 = Touch(2, 150, 100)
+        t2 = Touch(3, 250, 200)
+        r = uhdev.event([t0, t1, t2])
+        events = uhdev.next_sync_events()
+        self.debug_reports(r, uhdev, events)
+
+        # release the second
+        t1.tipswitch = False
+        r = uhdev.event([t1])
+        events = uhdev.next_sync_events()
+        self.debug_reports(r, uhdev, events)
+
+        # only the second is released
+        assert evdev.slots[0][libevdev.EV_ABS.ABS_MT_TRACKING_ID] != -1
+        assert evdev.slots[1][libevdev.EV_ABS.ABS_MT_TRACKING_ID] == -1
+        assert evdev.slots[2][libevdev.EV_ABS.ABS_MT_TRACKING_ID] != -1
+
+        # wait for the timer to kick in
+        time.sleep(0.2)
+
+        events = uhdev.next_sync_events()
+        self.debug_reports([], uhdev, events)
+
+        # now all 3 fingers are released
+        assert libevdev.InputEvent(libevdev.EV_KEY.BTN_TOUCH, 0) in events
+        assert evdev.slots[0][libevdev.EV_ABS.ABS_MT_TRACKING_ID] == -1
+        assert evdev.slots[1][libevdev.EV_ABS.ABS_MT_TRACKING_ID] == -1
+        assert evdev.slots[2][libevdev.EV_ABS.ABS_MT_TRACKING_ID] == -1
+
+
 class TestElanXPS9360(BaseTest.TestWin8Multitouch):
     def create_device(self):
         return Digitizer(
@@ -2086,3 +2132,12 @@ class Testsynaptics_06cb_ce08(BaseTest.TestPTP):
             input_info=(BusType.I2C, 0x06CB, 0xCE08),
             rdesc="05 01 09 02 a1 01 85 02 09 01 a1 00 05 09 19 01 29 02 15 00 25 01 75 01 95 02 81 02 95 06 81 01 05 01 09 30 09 31 15 81 25 7f 75 08 95 02 81 06 c0 c0 05 01 09 02 a1 01 85 18 09 01 a1 00 05 09 19 01 29 03 46 00 00 15 00 25 01 75 01 95 03 81 02 95 05 81 01 05 01 09 30 09 31 15 81 25 7f 75 08 95 02 81 06 c0 c0 06 00 ff 09 02 a1 01 85 20 09 01 a1 00 09 03 15 00 26 ff 00 35 00 46 ff 00 75 08 95 05 81 02 c0 c0 05 0d 09 05 a1 01 85 03 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 f8 04 75 10 55 0e 65 11 09 30 35 00 46 24 04 95 01 81 02 46 30 02 26 a0 02 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 f8 04 75 10 55 0e 65 11 09 30 35 00 46 24 04 95 01 81 02 46 30 02 26 a0 02 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 f8 04 75 10 55 0e 65 11 09 30 35 00 46 24 04 95 01 81 02 46 30 02 26 a0 02 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 f8 04 75 10 55 0e 65 11 09 30 35 00 46 24 04 95 01 81 02 46 30 02 26 a0 02 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 f8 04 75 10 55 0e 65 11 09 30 35 00 46 24 04 95 01 81 02 46 30 02 26 a0 02 09 31 81 02 c0 05 0d 55 0c 66 01 10 47 ff ff 00 00 27 ff ff 00 00 75 10 95 01 09 56 81 02 09 54 25 7f 95 01 75 08 81 02 05 09 09 01 25 01 75 01 95 01 81 02 95 07 81 03 05 0d 85 08 09 55 09 59 75 04 95 02 25 0f b1 02 85 0d 09 60 75 01 95 01 15 00 25 01 b1 02 95 07 b1 03 85 07 06 00 ff 09 c5 15 00 26 ff 00 75 08 96 00 01 b1 02 c0 05 0d 09 0e a1 01 85 04 09 22 a1 02 09 52 15 00 25 0a 75 08 95 01 b1 02 c0 09 22 a1 00 85 06 09 57 09 58 75 01 95 02 25 01 b1 02 95 06 b1 03 c0 c0 06 00 ff 09 01 a1 01 85 09 09 02 15 00 26 ff 00 75 08 95 14 91 02 85 0a 09 03 15 00 26 ff 00 75 08 95 14 91 02 85 0b 09 04 15 00 26 ff 00 75 08 95 45 81 02 85 0c 09 05 15 00 26 ff 00 75 08 95 45 81 02 85 0f 09 06 15 00 26 ff 00 75 08 95 03 b1 02 85 0e 09 07 15 00 26 ff 00 75 08 95 01 b1 02 c0",
         )
+
+class Testsynaptics_06cb_ce26(TestWin8TSConfidence):
+    def create_device(self):
+        return PTP(
+            "uhid test synaptics_06cb_ce26",
+            max_contacts=5,
+            input_info=(BusType.I2C, 0x06CB, 0xCE26),
+            rdesc="05 01 09 02 a1 01 85 02 09 01 a1 00 05 09 19 01 29 02 15 00 25 01 75 01 95 02 81 02 95 06 81 01 05 01 09 30 09 31 15 81 25 7f 75 08 95 02 81 06 c0 c0 05 0d 09 05 a1 01 85 03 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 45 05 75 10 55 0e 65 11 09 30 35 00 46 64 04 95 01 81 02 46 a2 02 26 29 03 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 45 05 75 10 55 0e 65 11 09 30 35 00 46 64 04 95 01 81 02 46 a2 02 26 29 03 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 45 05 75 10 55 0e 65 11 09 30 35 00 46 64 04 95 01 81 02 46 a2 02 26 29 03 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 45 05 75 10 55 0e 65 11 09 30 35 00 46 64 04 95 01 81 02 46 a2 02 26 29 03 09 31 81 02 c0 05 0d 09 22 a1 02 15 00 25 01 09 47 09 42 95 02 75 01 81 02 95 01 75 03 25 05 09 51 81 02 75 01 95 03 81 03 05 01 15 00 26 45 05 75 10 55 0e 65 11 09 30 35 00 46 64 04 95 01 81 02 46 a2 02 26 29 03 09 31 81 02 c0 05 0d 55 0c 66 01 10 47 ff ff 00 00 27 ff ff 00 00 75 10 95 01 09 56 81 02 09 54 25 7f 95 01 75 08 81 02 05 09 09 01 25 01 75 01 95 01 81 02 95 07 81 03 05 0d 85 08 09 55 09 59 75 04 95 02 25 0f b1 02 85 0d 09 60 75 01 95 01 15 00 25 01 b1 02 95 07 b1 03 85 07 06 00 ff 09 c5 15 00 26 ff 00 75 08 96 00 01 b1 02 c0 05 0d 09 0e a1 01 85 04 09 22 a1 02 09 52 15 00 25 0a 75 08 95 01 b1 02 c0 09 22 a1 00 85 06 09 57 09 58 75 01 95 02 25 01 b1 02 95 06 b1 03 c0 c0 06 00 ff 09 01 a1 01 85 09 09 02 15 00 26 ff 00 75 08 95 14 91 02 85 0a 09 03 15 00 26 ff 00 75 08 95 14 91 02 85 0b 09 04 15 00 26 ff 00 75 08 95 3d 81 02 85 0c 09 05 15 00 26 ff 00 75 08 95 3d 81 02 85 0f 09 06 15 00 26 ff 00 75 08 95 03 b1 02 85 0e 09 07 15 00 26 ff 00 75 08 95 01 b1 02 c0",
+        )

-- 
2.51.0

Re: [PATCH 0/2] HID: multitouch: fix sticky-fingers quirks

[Jiri Kosina]

On Wed, 8 Oct 2025, Benjamin Tissoires wrote:

> According to Peter, we've had for a very long time an issue on some
> mutltiouch touchpads where the fingers were stuck in a scrolling mode,
> or 3 fingers gesture mode. I was unable to debug it because it was
> rather hard to reproduce.
> 
> Recently, some people raised the issue again on libinput, and this time
> added a recording of the actual bug.
> 
> It turns out that the sticky finger quirk that was introduced back in
> 2017 was only checking the last report, and that those missing releases
> also happen when moving from 3 to 1 finger (only 1 is released instead
> of 2).
> 
> This solution seems to me to be the most sensible, because we could also
> add the NSMU quirk to win8 multitouch touchpads, but this would involve
> a lot more computations at each report for rather annoying corner cases.
> 
> Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/1194
> Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
> ---
> Benjamin Tissoires (2):
>       HID: multitouch: fix sticky fingers
>       selftests/hid: add tests for missing release on the Dell Synaptics
> 
>  drivers/hid/hid-multitouch.c                       | 27 ++++++-----
>  .../testing/selftests/hid/tests/test_multitouch.py | 55 ++++++++++++++++++++++
>  2 files changed, 69 insertions(+), 13 deletions(-)

Now queued in for-6.18/upstream-fixes. Thanks,

-- 
Jiri Kosina
SUSE Labs