Hot to initialize LTE module using libqmi and systemd-network (networkd-dispatcher)

Question

I want to initialize the lte module using libqmi and networkd-dispatcher. What I got so far is a shell script which is located at /etc/networkd-dispatcher/degraded.d/01-wwan.sh

     #!/bin/bash
    
    interface="${IFACE}"
    
    if [[ "$interface" == *"wwan"* ]]; then
      device="/dev/cdc-wdm${interface: -1}"
      is_wwan="y"
    fi
    
    if [[ "$is_wwan" == "y" ]]; then
      ip link set dev "${interface}" down
      echo "Y" > "/sys/class/net/${interface}/qmi/raw_ip"
      qmi-network "${device}" start || true
      qmicli -p -d "${device}" --wds-set-autoconnect-settings=enabled || true
      ip link set dev "${interface}" up
    fi

My problem now is that this script is called over and over again sometimes after an reboot and takes some time to be stable. I thought if I add a sleep 10s after taking it link up it solves the issue, but it doesn't. Any suggestions how to fix this?

score 1 · Accepted Answer · answered Sep 23 '22 at 07:53

Sorry it's a bit late but just came across this question.

If just for the sake of completeness, a method that I found to be quite predictable and reliable is to link a systemd service file that starts a script with a udev rule:

Create a file in /etc/udev/rules.d, for example 10-lte-modem.rules, which should look like this:

SUBSYSTEM=="net",ACTION=="add",ENV{PRODUCT}=="PID-of-modem", TAG+="systemd",ENV{SYSTEMD_WANTS}

Note you can use different triggers, for example if your modem is at a fixed port on a usb hub then you can use KERNELS="1-1.1". The point is to trigger the systemd service on the enumeration of the modem (which allows you to reboot the modem and your script will automatically re-run). You also might have to add in a NAME= field to give your interface a deterministic name.

In your systemd service file that will start your script, you have something like:

[Unit]
ConditionPathExists=|!/sys/class/net/wwan1
ConditionPathExists=|!/sys/class/net/wwan2

[Service]
Type=simple
Restart=always
RemainAfterExit=no
ExecStart=/bin/sh /etc/networkd-dispatcher/degraded.d/01-wwan.sh

The |! syntax in systemd allows you to OR different conditions.

Depending on the exact setup of your system, like whether its a PCIe modem or USB, you might have to play around with the udev and systemd settings to get what you want, but I've found it results in very stable behaviour.

Hot to initialize LTE module using libqmi and systemd-network (networkd-dispatcher)

1 Answers1