touchpanel inputs stop being propagated to the core pointer?

[Peter Hutterer]

On Mon, Mar 14, 2022 at 09:36:08PM +0100, Roland Freikamp wrote:
> Hi,
> 
> I have a problem with the input-system:
> - X suddenly stops to accept touches from a touchpanel
>   (connected via USB).
> - Re-connecting USB re-enables the touchpanel.
> - "xinput disable 7; xinput enable 7" (7=id of the touchpanel) also
>   re-enables the touchpanel.
> 
> It looks like the input-events of the touchpanel suddenly stop to be
> propagated to the "Virtual core pointer":
> - "xinput list --long 7" still shows the touches and correct positions
> - but the positions in 'xinput list --long "Virtual core pointer"' are frozen
> 
> Any ideas/hints?

two possible causes I can think of:
- a stuck grab on the device itself (unlikely since virtually nothing grabs
  devices directly). stuck grabs are fun to debug (fsvo "fun"), unless you
  have a reliable reproducer it's virtually impossible.
- the device loses track of touch events and either the device or X thinks
  that there is more than one touch down. Happened frequently with older
  touchpanels. You can verify that by running libinput record --autorestart
  (see the man page) and check the most recent recording(s) when it happens.
  If you see BTN_TOOL_DOUBLETAP appearing when you have only one finger down,
  the issue is in the device itself.

Cheers,
  Peter