[Wayland-bugs] [Bug 96925] Touchpad tap doesn't work on DELL XPS 15 9550

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96925

--- Comment #7 from Peter Hutterer <peter.hutterer at who-t.net> ---
(In reply to Russell Stuart from comment #5)
> > if that detects the taps as button presses
> 
> I think this means it does:
> 
> $ sudo libinput-debug-events --enable-tap
> event5 	DEVICE_ADDED     Power Button                      seat0 default
> group1 cap:k
> event9 	DEVICE_ADDED     Video Bus                         seat0 default
> group2 cap:k
> event10	DEVICE_ADDED     Video Bus                         seat0 default
> group2 cap:k
> event3 	DEVICE_ADDED     Power Button                      seat0 default
> group3 cap:k
> event4 	DEVICE_ADDED     Sleep Button                      seat0 default
> group4 cap:k
> event7 	DEVICE_ADDED     Integrated_Webcam_HD              seat0 default
> group5 cap:k
> event6 	DEVICE_ADDED     ELAN Touchscreen                  seat0 default
> group6 cap:t	size 333.50/188.50mm calib
> event15	DEVICE_ADDED     DLL06E4:01 06CB:7A13 Touchpad     seat0 default
> group7 cap:pg	size 102.33/77.33mm tap(dl off) left scroll-nat
> scroll-2fg-edge click-buttonareas-clickfinger dwt-on
> event0 	DEVICE_ADDED     AT Translated Set 2 keyboard      seat0 default
> group8 cap:k
> event1 	DEVICE_ADDED     SynPS/2 Synaptics TouchPad        seat0 default
> group9 cap:pg	size 106.98/80.00mm tap(dl off) left scroll-nat
> scroll-2fg-edge click-buttonareas-clickfinger dwt-on
> event15	POINTER_BUTTON    +1.10s	BTN_LEFT (272) pressed, seat count: 1
> event15	POINTER_BUTTON    +1.37s	BTN_LEFT (272) released, seat count: 0

yes, that's a left button press. you should see right and middle buttons for
2 and 3 finger taps, respectively too then.

> It isn't the case on boot:

tapping is disabled by default, see
https://wayland.freedesktop.org/libinput/doc/latest/tapping.html

You'll have to enable it, either with an xorg.conf snippet (see man
libinput, option Tapping) or have something set it for you (like gnome does
when the toggle is flipped). alternatively, you can manually set it through
libinput through some startup script, but that's flaky and not really
recommended.

> So I execute:
> 
> $ xinput set-prop 15 281 1

fwiw, a better approach would be:
    xinput set-prop "SynPS/2 Synaptics TouchPad" "libinput Tapping Enabled" 1
which will work even when the device ID changes and is a lot more obvious
than the pure property numbers.
http://who-t.blogspot.com.au/2016/07/xinput-resolves-device-names-and.html

> $ xinput list-props 15
> Device 'SynPS/2 Synaptics TouchPad':

ok, the reason is that your touchpad has two devices, one of which never
sends events. that's a side-effect of the i2c kernel implementation, check
the event node in the libinput output above: all the events come from
event15 which is the "DLL06E4:01 06CB:7A13 Touchpad" device. So if you run
the xinput command against that device it'll work.

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