Unwanted touchpad movements on tap with Synaptics touchpad on DELL Inspiron-3521

[Dario Menin]

https://gitlab.freedesktop.org/libinput/libinput/issues/199

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When using the touchpad, the mouse cursor moves even when keeping the finger still on one point.

Triggering the behaviour: this happens when the contact surface is very small, so it gets triggered for example when tapping on a button, right before the finger leaves the touchpad. This makes clicking buttons using the touchpad (for example, the "x" button in the browser tabs) very difficult.

In attachment, an evemu-record done keeping the finger on one point, barely touching the touchpad.

The recording was done with the command:

sudo evemu-record > touchpad.evemu
Available devices:
/dev/input/event0: Power Button
/dev/input/event1: Lid Switch
/dev/input/event2: Power Button
/dev/input/event3: AT Translated Set 2 keyboard
/dev/input/event4: Video Bus
/dev/input/event8: SynPS/2 Synaptics TouchPad
/dev/input/event9: Dell WMI hotkeys
/dev/input/event10: HDA Intel PCH Mic
/dev/input/event11: HDA Intel PCH Front Headphone
/dev/input/event12: HDA Intel PCH HDMI/DP,pcm=3
/dev/input/event13: Laptop_Integrated_Webcam_HD: In
Select the device event number [0-13]: 8

To replay the recording (the strange behaviour is particularly visible in the final part):

sudo evemu-play /dev/input/event8 < touchpad.evemu

(replace event8 with your input device)

System info:

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

apt-cache policy libinput10
libinput10:
  Installato: 1.10.4-1
  Candidato: 1.10.4-1
  Tabella versione:
 *** 1.10.4-1 500
        500 http://it.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status

apt-cache policy libinput-bin
libinput-bin:
  Installato: 1.10.4-1
  Candidato: 1.10.4-1
  Tabella versione:
 *** 1.10.4-1 500
        500 http://it.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status

[Daniel van Vugt (vanvugt)]

Could you please try live booting (no need to install) Ubuntu 18.10 and tell us if the newer version of libinput there is any better?

  http://releases.ubuntu.com/18.10/

If it's not then please report the bug to the libinput developers here:

  https://gitlab.freedesktop.org/groups/libinput/-/issues

and tell us the new bug ID.

[Dario Menin (darioalessio-menin)]

Hi, with 18.10 (live session) the behaviour is the same. I opened: https://gitlab.freedesktop.org/libinput/libinput/issues/199.

Let me know if you need further information.

[Dario Menin (darioalessio-menin)]

Don't know if this is related:

Here https://wayland.freedesktop.org/libinput/doc/latest/touchpad-jitter.html#overriding-the-hysteresis-margins I found something about jitter, but if I run:

sudo libinput measure fuzz /dev/input/event5

I get:

Using SynPS/2 Synaptics TouchPad: /dev/input/event5
Traceback (most recent call last):
  File "/usr/lib/x86_64-linux-gnu/libinput/libinput-measure-fuzz", line 445, in main
    fuzz = device.check_property()
  File "/usr/lib/x86_64-linux-gnu/libinput/libinput-measure-fuzz", line 113, in check_property
    raise InvalidConfigurationError('fuzz for ABS_X differs from ABS_MT_POSITION_X')
__main__.InvalidConfigurationError: fuzz for ABS_X differs from ABS_MT_POSITION_X

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/x86_64-linux-gnu/libinput/libinput-measure-fuzz", line 464, in <module>
    main(sys.argv)
  File "/usr/lib/x86_64-linux-gnu/libinput/libinput-measure-fuzz", line 458, in main
    print('Error: {}'.format(e.message))
AttributeError: 'InvalidConfigurationError' object has no attribute 'message'