Relatively working libinput configuration for the touchpad on Dell XPS 9320 running Ubuntu.

40-libinput.conf

# Match on all types of devices but joysticks
#
# If you want to configure your devices, do not copy this file.
# Instead, use a config snippet that contains something like this:
#
# Section "InputClass"
#   Identifier "something or other"
#   MatchDriver "libinput"
#
#   MatchIsTouchpad "on"
#   ... other Match directives ...
#   Option "someoption" "value"
# EndSection
#
# This applies the option any libinput device also matched by the other
# directives. See the xorg.conf(5) man page for more info on
# matching devices.

Section "InputClass"
        Identifier "libinput pointer catchall"
        MatchIsPointer "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput keyboard catchall"
        MatchIsKeyboard "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput touchpad catchall"
        MatchIsTouchpad "on"
        MatchDevicePath "/dev/input/event*"
	Option "Tapping" "true"
	Option "TappingDrag" "true"
	Option "DisableWhileTyping" "true"
	Option "AccelProfile" "adaptive"
	Option "AccelSpeed" "0.4"
	Option "SendEventsMode" "disabled-on-external-mouse"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput touchscreen catchall"
        MatchIsTouchscreen "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput tablet catchall"
        MatchIsTablet "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection