How to work with input devices#

In our reference distribution simplecore-distro we are using libinput for handling input from devices like

touchscreens
mice
keyboards
GPIO based input devices

by default each device found at runtime will form a /dev/input/eventX (X is a natural number).

The mapping of device to the eventX entry can be found by running on the device

$ /usr/libexec/libinput/libinput-list-devices

Device:           Power Button
Kernel:           /dev/input/event0
Group:            2
Seat:             seat0, default
Capabilities:     keyboard
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      n/a
Nat.scrolling:    n/a
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Accel profiles:   n/a
Rotation:         n/a

Device:           i2c_designware
Kernel:           /dev/input/event13
Group:            5
Seat:             seat0, default
Capabilities:     keyboard pointer
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      n/a
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Accel profiles:   n/a
Rotation:         n/a

in this example the i2c_designware device would be connected to /dev/input/event13.

Debugging libinput events#

In case you want to debug the events published by the device, you can use one of the following tools:

libinput-record#

This tool allows you to record the events posted by an input device to console or a file.

$ /usr/libexec/libinput/libinput-record <event device>

so for above’s example

$ /usr/libexec/libinput/libinput-record /dev/input/event13

libinput-debug-events#

A slightly different tool from libinput allows you to have all events logged to console

$ /usr/libexec/libinput/libinput-debug-events <event device>

evtest as an alternative#

As an alternative you can use evtest to debug events posted to libinput

$ evtest

then just follow the on-screen instructions.

Setting input device classification#

libinput makes a few assumptions on what type of device. Choices are

mouse
keyboard
touchpad
touchscreen
tablet

It could happen that the automatic detection misclassifies a device. Read the following chapters to override the automatic choices by libinput.

Getting device classification#

The device type is added by udev and libinput and can be checked by running

$ udevadm info -n <event device>

for our above’s example that would look like

$ udevadm info -n /dev/input/event13
N: input/event13
L: 0
S: input/by-path/pci-0000:00:15.1-platform-i2c_designware.1-event-mouse
E: DEVPATH=/devices/pci0000:00/0000:00:15.1/i2c_designware.1/i2c-2/0018:0488:1024.0001/input/input16/event13
E: DEVNAME=/dev/input/event13
E: MAJOR=13
E: MINOR=77
E: SUBSYSTEM=input
E: USEC_INITIALIZED=10229073
E: ID_INPUT=1
E: ID_INPUT_TOUCHPAD=1
E: ID_INPUT_WIDTH_MM=110
E: ID_INPUT_HEIGHT_MM=63
E: ID_SERIAL=noserial
E: ID_PATH=pci-0000:00:15.1-platform-i2c_designware.1
E: ID_PATH_TAG=pci-0000_00_15_1-platform-i2c_designware_1

of importance are here the ID_INPUT_* tags.

Overriding the defaults#

To override the defaults you would need to add a custom udev rule. Create a file /etc/udev/rules.d/00-my-rules.conf

ACTION=="add|change", KERNEL=="event[0-9]*", \
DEVPATH=="/devices/pci0000:00/0000:00:15.1/i2c_designware.1/i2c-2/0018:0488:1024.0001/input/input16/event13", \
ENV{ID_INPUT_TABLET}="", \
ENV{ID_INPUT_TOUCHPAD}="1", \
ENV{ID_INPUT_TOUCHSCREEN}="0", \
ENV{ID_INPUT_MOUSE}="", \
ENV{EVDEV_UDEV_TAG_TABLET_PAD}=""

Every ENV{ID_INPUT_*}="" operation unsets a previously set classification. Every ENV{ID_INPUT_*}="1" sets a classification flags.

So in this example we force a classification as a touchpad.

Further information on classification types can be found here.