From: DaytonCL artem749507@gmail.com
[ Upstream commit ff3f234ff1dcd6d626a989151db067a1b7f0f215 ]
Some VTL-class touchpads (e.g. TOPS0102:00 35CC:0104) intermittently fail to release a finger contact. A previous slot remains logically active, accompanied by stale BTN_TOOL_DOUBLETAP state, causing gestures to stay latched and resulting in stuck two-finger scrolling and false right-clicks.
Apply MT_QUIRK_STICKY_FINGERS to handle the unreleased contact correctly.
Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/1225 Suggested-by: Benjamin Tissoires benjamin.tissoires@redhat.com Tested-by: DaytonCL artem749507@gmail.com Signed-off-by: DaytonCL artem749507@gmail.com Signed-off-by: Benjamin Tissoires bentiss@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
## Analysis of HID Multitouch Quirk Addition
### 1. COMMIT MESSAGE ANALYSIS
The commit clearly describes a **real user-visible bug**: - VTL-class touchpads (specifically TOPS0102:00 35CC:0104) intermittently fail to release finger contacts - This causes gestures to stay latched - stuck two-finger scrolling and false right-clicks - Links to a libinput bug report: https://gitlab.freedesktop.org/libinput/libinput/-/issues/1225 - Has `Tested-by:` from the reporter and `Suggested-by:` from Benjamin Tissoires (HID maintainer) - Signed off by the maintainer (Benjamin Tissoires)
### 2. CODE CHANGE ANALYSIS
The change is **extremely minimal** - adding one line: ```c MT_QUIRK_STICKY_FINGERS | ```
to the existing `MT_CLS_VTL` class definition. This enables an already- existing quirk flag (`MT_QUIRK_STICKY_FINGERS`) for VTL-class devices.
The quirk mechanism handles cases where a touchpad firmware fails to properly report when a finger has been lifted. Without it, the system thinks the finger is still touching, causing "sticky" gestures. The quirk infrastructure already exists and is well-tested - this commit just enables it for another device class.
### 3. CLASSIFICATION
This falls squarely into the **QUIRKS and WORKAROUNDS exception category**: - Hardware-specific quirk for buggy/non-compliant devices - The quirk code already exists in mainline - only enabling it for VTL class - Fixes real-world hardware behavior issues
This is NOT: - A new feature or API - A new driver - Code refactoring
### 4. SCOPE AND RISK ASSESSMENT
| Factor | Assessment | |--------|------------| | Lines changed | 1 | | Files touched | 1 | | Complexity | Trivially low | | Subsystem | HID multitouch (mature, stable) | | Risk | Very low |
The worst case scenario: if the quirk somehow caused issues on a specific VTL device, it would only affect that device class. But the current behavior is already broken for affected users, so this is a clear improvement.
### 5. USER IMPACT
- **Affected users**: Anyone with VTL-class touchpads - **Symptoms**: Stuck two-finger scrolling, false right-clicks - these are highly disruptive daily-use issues - **Severity**: Medium-high for affected users (makes touchpad unreliable) - **Evidence of real impact**: Linked bug report from libinput tracker
### 6. STABILITY INDICATORS
- `Tested-by:` tag from the reporter who experienced the issue - Suggested and signed off by HID subsystem maintainer - The `MT_QUIRK_STICKY_FINGERS` quirk has existed since ~Linux 3.15 - The `MT_CLS_VTL` class has existed since ~Linux 4.13 - Well-established quirk pattern used by many other device classes (FLATFROG, LG, ASUS, etc.)
### 7. DEPENDENCY CHECK
- **No dependencies** on other commits - Both the quirk flag and VTL class exist in all recent stable trees - Should apply cleanly without modification
### STABLE KERNEL RULES ASSESSMENT
| Criterion | Met? | |-----------|------| | Obviously correct and tested | ✅ Yes - trivial change, has Tested-by | | Fixes a real bug | ✅ Yes - documented hardware issue with bug report | | Important issue | ✅ Yes - stuck gestures/false clicks affect daily use | | Small and contained | ✅ Yes - 1 line in 1 file | | No new features | ✅ Yes - uses existing quirk mechanism | | Applies cleanly | ✅ Yes - no dependencies |
### CONCLUSION
This is an **ideal stable backport candidate**:
1. **Minimal risk**: Single-line addition of an existing, well-tested quirk flag 2. **Real user benefit**: Fixes stuck gestures and false clicks on VTL touchpads 3. **Proper testing**: Has Tested-by tag and maintainer approval 4. **Falls under hardware quirk exception**: Hardware quirks/workarounds are explicitly allowed in stable even though they add code 5. **Self-contained**: No dependencies, applies cleanly to stable trees
The fix is small, surgical, obviously correct, and addresses a real user-visible hardware issue. This is exactly the type of hardware quirk addition that stable trees should accept.
**YES**
drivers/hid/hid-multitouch.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c index 179dc316b4b51..a0c1ad5acb670 100644 --- a/drivers/hid/hid-multitouch.c +++ b/drivers/hid/hid-multitouch.c @@ -393,6 +393,7 @@ static const struct mt_class mt_classes[] = { { .name = MT_CLS_VTL, .quirks = MT_QUIRK_ALWAYS_VALID | MT_QUIRK_CONTACT_CNT_ACCURATE | + MT_QUIRK_STICKY_FINGERS | MT_QUIRK_FORCE_GET_FEATURE, }, { .name = MT_CLS_GOOGLE,