[Wayland-bugs] [Bug 89800] More than 4 fingers results in "invalid event, no fingers are down"

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89800

            Bug ID: 89800
           Summary: More than 4 fingers results in "invalid event, no
                    fingers are down"
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: killertofu at gmail.com

When running the 'event-debug' tool with an Intuos Pro, the message "libinput
error: libinput bug: invalid event, no fingers are down" will appear several
times after placing a fifth finger on the touchpad.

Running the tool with GDB, it appears that the "if we have too many touches"
case inside 'tp_unhover_touches' (evdev-mt-touchpad.c) is satisfied and
subsequently clears out all active touches once the fifth finger goes down.
This is because "nfake_touches" should be zero at this point due to the kernel
switching out BTN_TOOL_QUADTAP for BTN_TOOL_QUINTTAP (which isn't handled by
libinput).

This error can be delayed until 6 fingers are in contact by handling
BTN_TOOL_QUINTTAP, but it isn't really a solution (that's the last *TAP tool
reported by the kernel, and the touchpad can report far more). Libinput needs
to sense when the *TAP tool "overflows" and rely on slot state instead.

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