Disabling the panel of a touchscreen does not disable the input/touch part wasting energy
[This follows up on How to disable the touchscreen so it does not draw power? and libinput issue 956.]
Summary
Monitoring the power usage of a Dell XPS 13 9360 with a touchscreen, while an external monitor is connected and the laptop monitor disabled, it turned out, the ELAN touchscreen still consumes power although unlikely being used. Hans de Goede replied with:
Ideally userspace would close the /dev/input/event node belonging to the touchscreen when the internal panel is off. Please file an issue for that against libinput (to add the plumbing for this to libinput, ultimately the wayland-compositor, e.g. mutter, then needs to use that plumbing).
In the libinput issue Peter Hutterer replied:
libinput does close the fds when the device is switched to
LIBINPUT_CONFIG_SEND_EVENTS_DISABLED
which should do the trick. So the libinput bits are ready, the rest is up to the next layer in the stack, i.e. the compositor (e.g. mutter). So I think at least the libinput side is done.