On 08/11/2017 02:44 AM, Dmitry Torokhov wrote:
Changing the tool identity to signal the tool property of low confidence
does not seem quite right to me. Using MT_TOOL_PALM forces a semantic
distinction between tool identity and touch state, which userland seems
unprepared for. The additional kernel state needed to make it work
raises the question if more considerations will turn up over with time.
According to Microsoft specification  for Precision Touchpads (and
Touchscreens) the devices use "confidence" reports to signal accidental
touches, or contacts that are "too large to be a finger". Instead of
simply marking contact inactive in this case (which causes issues if
contact was originally proper and we lost confidence in it later, as
this results in accidental clicks, drags, etc), let's report such
contacts as MT_TOOL_PALM and let userspace decide what to do.
Additionally, let's report contact size for such touches as maximum
allowed for major/minor, which should help userspace that is not yet
aware of MT_TOOL_PALM to still perform palm rejection.
An additional complication, is that some firmwares do not report
non-confident touches as active. To cope with this we delay release of
such contact (i.e. if contact was active we first report it as still
active MT+TOOL_PALM and then synthesize the release event in a separate
Why not add a property event, like BTN_TOOL_PALM, instead? In other
words, modifying the definition of "active" as you propose, but then use
a BTN_TOOL_PALM property to signal "s->confidence_state"? It perhaps
creates a different oddity for applications unaware of palm, but AFAICT,
it would not complicate the notion of touch state. Or?