0. 停止 ModemManager，避免它在基带重启期间不断访问设备

systemctl stop ModemManager

1. 停止modem

echo stop > /sys/class/remoteproc/remoteproc0/state
cat /sys/class/remoteproc/remoteproc0/state

命令应该返回 offline 的状态
2. 启动modem

echo start > /sys/class/remoteproc/remoteproc0/state
cat /sys/class/remoteproc/remoteproc0/state

状态应该恢复为 running
3. 启动ModemManager

systemctl start ModemManager

4. 等待10秒左右, 查看modem是否可用

mmcli -L