Commit b5e65ae557da ("HID: multitouch: Add quirk for Hantick 5288
touchpad") assigned MT_CLS_NSMU to the HTIX5288 (0911:5288).  This was
necessary because the device sometimes fails to send touch release
signals when transitioning from >=2 fingers to <2 fingers, and
MT_QUIRK_NOT_SEEN_MEANS_UP fixes stuck touches by treating missing
contacts as released.

However, MT_CLS_NSMU only carries MT_QUIRK_NOT_SEEN_MEANS_UP.  It
lacks MT_QUIRK_CONTACT_CNT_ACCURATE and MT_QUIRK_IGNORE_DUPLICATES.
As a result, after a two-finger scroll finger lift, the device still
reports stale coordinates from the released contact in subsequent
frames, and the driver overwrites the remaining active slot with
those frozen coordinates.  The remaining finger appears stuck at the
lift position until all fingers are lifted.

This was confirmed via evtest on Arch Linux 7.1.3: after
TRACKING_ID=-1 for the released slot, every subsequent frame contained
duplicate position pairs -- the real moving finger's coordinates
followed by the lifted finger's frozen position, both attributed to
the active slot.

Reclassify the device to MT_CLS_WIN_8_FORCE_MULTI_INPUT_NSMU
(0x0018), which preserves the original MT_QUIRK_NOT_SEEN_MEANS_UP
fix while adding the necessary Win8 quirks (CONTACT_CNT_ACCURATE,
IGNORE_DUPLICATES), preventing stale coordinate contamination.

The additional FORCE_MULTI_INPUT flag is harmless here: it separates
the mouse and touchpad collections into distinct input devices,
which is the standard behavior libinput already expects.

Fixes: b5e65ae557da ("HID: multitouch: Add quirk for Hantick 5288 touchpad")
Signed-off-by: Xianglin Lin <redacted>
---
 drivers/hid/hid-multitouch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c

@@ -2722,7 +2722,7 @@ static const struct hid_device_id mt_devices[] = {
 			HID_ANY_ID) },
 
 	/* Hantick */
-	{ .driver_data = MT_CLS_NSMU,
+	{ .driver_data = MT_CLS_WIN_8_FORCE_MULTI_INPUT_NSMU,
 		HID_DEVICE(BUS_I2C, HID_GROUP_MULTITOUCH_WIN_8,
 			   I2C_VENDOR_ID_HANTICK, I2C_PRODUCT_ID_HANTICK_5288) },
 

-- 
2.55.0