==== udevadm ====
=== reloading rules ===
<code bash>udevadm control --reload-rules</code>
<code bash>udevadm control --reload-rules && udevadm trigger</code>

=== Testing rules ===
<code bash>udevadm test /sys/class/tty/ttyACM0</code>

NOTE: This program is for debugging only, it does not run any program specified by a RUN key. It may show incorrect results, because some values may be different, or not available at a simulation run.

==== Getting info ====
<code bash>
udevadm info --attribute-walk --path=/sys/class/tty/ttyACM0
udevadm info --attribute-walk --name=/dev/ttyUSB0
</code>

=== Get Telit modem serial number ===
<code bash>
udevadm info -q property -n /dev/ttyACM1 | grep ID_SERIAL_SHORT
ID_SERIAL_SHORT=356136070718830
</code>

==== Debug ====
<file | /etc/udev/udev.conf>
udev_log="debug"
</file>

<code bash>
udevadm control --log-priority=debug

</code>

==== Rules ====
=== Order ===

>Files should be named xx-descriptive-name.rules, the xx should be chosen first according to the following sequence points:
>
> < 60  most user rules; if you want to prevent an assignment being overriden by default rules, use the := operator.
>
>these cannot access persistent information such as that from vol_id
>
>< 70  rules that run helpers such as vol_id to populate the udev db
>
>< 90  rules that run other programs (often using information in the udev db)
>
> >=90  rules that should run last


==== Executing commands ====
Triggering commands should be done using RUN, because it is executed after all systemd actions.
<code>
SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="0", RUN+="/usr/bin/true"
SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="1", RUN+="/usr/bin/true"
</code>

**RUN vs PROGRAM**

PROGRAM is used to return device name, e.g. to return name for symlink. It is called during device setup, so it is not good place to execute external tools.


<code>
ACTION=="add", DRIVERS=="usb", ATTRS{manufacturer}=="Telit", ATTRS{idVendor}=="1bc7", ATTRS{idProduct}=="0021", PROGRAM="/bin/sh -c '/bin/echo -e {\\042imei\\042:\\042%s{serial}\\042} > /etc
/imei.json'"
</code>

=== Shell ENV ===
<code bash>
ID_BUS=usb
DEVNAME=/dev/ttyACM0
ID_VENDOR_FROM_DATABASE=Telit Wireless Solutions
ACTION=add
ID_SERIAL_SHORT=356611070046259
ID_USB_DRIVER=cdc_acm
ID_TYPE=generic
MAJOR=166
DEVPATH=/devices/platform/ocp/47400000.usb/47401c00.usb/musb-hdrc.0.auto/usb1/1-1/1-1:1.0/tty/ttyACM0
ID_MODEL_ENC=FIH7160
ID_USB_INTERFACES=:020201:0a0000:020d00:0a0001:
ID_MODEL=FIH7160
DEVLINKS=/dev/serial/by-path/platform-musb-hdrc.0.auto-usb-0:1:1.0 /dev/serial/by-id/usb-Telit_FIH7160_356611070046259-if00
ID_SERIAL=Telit_FIH7160_356611070046259
SUBSYSTEM=tty
ID_MODEL_ID=0036
MINOR=0
ID_PATH=platform-musb-hdrc.0.auto-usb-0:1:1.0
ID_MODEL_FROM_DATABASE=LE910 V2
ID_VENDOR_ENC=Telit
ID_PATH_TAG=platform-musb-hdrc_0_auto-usb-0_1_1_0
ID_VENDOR=Telit
ID_USB_INTERFACE_NUM=00
ID_VENDOR_ID=1bc7
ID_REVISION=1730
</code>


=== Creating device symlinks ===
<code>
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ENV{ID_INPUT_TOUCHSCREEN}=="1", ATTRS{name}=="edt-ft53*", SYMLINK+="input/touchscreen", OPTIONS+="link_priority=100"
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ENV{ID_INPUT_TOUCHSCREEN}=="1", ATTRS{name}=="ti-tsc",    SYMLINK+="input/touchscreen", OPTIONS+="link_priority=0"
</code>
''link_priority'': higher has higher priority

Define symlink name in device tree (add property ''symlink'') i.e:
<code>
&pwm4 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_pwm4>;
	status = "okay";
	symlink = "buzzer";
};
</code>

<code>
ATTR{device/of_node/symlink}!="", ENV{DEVNAME}!="", SYMLINK+="%s{device/of_node/symlink}"
</code>

See:
  - [[https://github.com/mvduin/py-uio/blob/master/dts/pwmss2.dtsi#L122|pwmss2.dtsi]]
  - [[https://github.com/mvduin/py-uio/blob/master/etc/udev/rules.d/10-of-symlink.rules|10-of-symlink.rules]]
  - [[https://github.com/mvduin/py-uio/blob/master/dts/pwmss2.dtsi|pwmss2.dtsi]]

=== Triggering systemd ===
<code>
SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="0", TAG+="systemd", ENV{SYSTEMD_WANTS}="powersaving.service"
SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="1", TAG+="systemd", ENV{SYSTEMD_WANTS}="powersaving.service"
SUBSYSTEM=="printer", TAG+="systemd", ENV{SYSTEMD_WANTS}="printer.target"
</code>

More info about systemd interactions: [[https://www.freedesktop.org/software/systemd/man/latest/systemd.device.html|systemd.device — Device unit configuration]]

=== Prevent ModemManager ===
<file | /etc/udev/rules.d/99-nomm.rules>
ATTRS{idVendor}=="0451" ATTR{idProduct}=="bef3", ENV{ID_MM_DEVICE_IGNORE}="1"
</file>