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HID: multitouch: Honor ContactCount for Yoga Book 9 to suppress ghost contacts

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The INGENIC 17EF:6161 firmware on the Lenovo Yoga Book 9 14IAH10
does not clear stale contact slots when fingers are lifted.  Each
HID report contains up to 10 finger slots, but only the first
ContactCount slots represent valid contacts; the remaining slots
retain TipSwitch=1 with positions from previous touches.

Raw HID capture confirms this: across a 60-second capture with
repeated multi-finger gestures, 90% of frames had more TipSwitch=1
slots than the reported ContactCount.  The ContactCount field itself
is always accurate.

Add MT_QUIRK_CONTACT_CNT_ACCURATE to the MT_CLS_YOGABOOK9I class so
the driver stops processing slots once ContactCount valid contacts
have been consumed, discarding the stale ghost entries per HID
specification section 17.  MT_QUIRK_NOT_SEEN_MEANS_UP (already in
the class) ensures that any slot skipped by this guard is released
via INPUT_MT_DROP_UNUSED at frame sync.

Signed-off-by: Dave Carey <carvsdriver@gmail.com>
Tested-by: Dave Carey <carvsdriver@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
This commit is contained in:
Dave Carey 2026-05-14 15:32:58 -04:00 committed by Jiri Kosina
parent f1bd44b9b6
commit ef257b8be9
1 changed files with 1 additions and 0 deletions
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1
drivers/hid/hid-multitouch.c
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@ -445,6 +445,7 @@ static const struct mt_class mt_classes[] = {
{ .name = MT_CLS_YOGABOOK9I,
.quirks = MT_QUIRK_NOT_SEEN_MEANS_UP |
MT_QUIRK_ALWAYS_VALID |
MT_QUIRK_CONTACT_CNT_ACCURATE |
MT_QUIRK_FORCE_MULTI_INPUT |
MT_QUIRK_SEPARATE_APP_REPORT |
MT_QUIRK_HOVERING |