Simcom modem on Fedora IoT using ModemManager and NetworkManager

I'm trying to get a simcom7080 cellular modem to work with ModemManager(mm) and NetworkManager(nm) on Fedora IoT 41.

I followed this guide for setting up the modem and network connection.

The modem is recognized by mm but I can't seem to create a valid connection for it using nm.

Here's the output from mm. Note that driver is cdc_ether and there's a network interface enu1u4i4 in the ports section.

[root@localhost ~]# mmcli -m 8
  --------------------------------
  General  |                 path: /org/freedesktop/ModemManager1/Modem/8
           |            device id: [[ *** ]]
  --------------------------------
  Hardware |         manufacturer: SIMCOM_Ltd
           |                model: SIMCOM_SIM7080
           |    firmware revision: Revision:1951B16SIM7080
           |            supported: gsm-umts, lte
           |              current: gsm-umts, lte
           |         equipment id: [[ *** ]]
  --------------------------------
  System   |               device: /sys/devices/platform/scb/fe9c0000.xhci/usb1/1-1/1-1.4
           |              physdev: /sys/devices/platform/scb/fe9c0000.xhci/usb1/1-1/1-1.4
           |              drivers: option, cdc_ether
           |               plugin: simtech
           |         primary port: ttyUSB2
           |                ports: enu1u4i4 (net), ttyUSB0 (ignored), ttyUSB1 (gps),
           |                       ttyUSB2 (at), ttyUSB3 (at)
  --------------------------------
  Status   |       unlock retries: sim-pin (3), sim-puk (3), sim-pin2 (3), sim-puk2 (3)
           |                state: registered
           |          power state: on
           |          access tech: hspa
           |       signal quality: 100% (recent)
  --------------------------------
  Modes    |            supported: allowed: 2g; preferred: none
           |              current: allowed: 2g; preferred: none
  --------------------------------
  IP       |            supported: ipv4, ipv6, ipv4v6, non-ip
  --------------------------------
  3GPP     |                 imei: [[ *** ]]
           |          operator id: 24007
           |        operator name: Tele2
           |         registration: roaming
           | packet service state: attached
  --------------------------------
  3GPP EPS | ue mode of operation: csps-2
  --------------------------------
  SIM      |     primary sim path: /org/freedesktop/ModemManager1/SIM/8
  --------------------------------
  Bearer   |                paths: /org/freedesktop/ModemManager1/Bearer/4
           |                       /org/freedesktop/ModemManager1/Bearer/3
           |                       /org/freedesktop/ModemManager1/Bearer/2

I then create a connection using nmcli ...

[root@localhost ~]# nmcli connection add con-name "wwan" ifname "*" type gsm
[root@localhost ~]# nmcli connection
NAME                UUID                                  TYPE      DEVICE
Wired connection 1  5d772a4c-6b03-350e-a74b-351c797c3af7  ethernet  end0
wwan                fed0a42d-c186-4f6b-93c3-d63c4a23ce6a  gsm       ttyUSB2
lo                  fd6aaf68-7634-4b2f-a26b-62d4d73629af  loopback  lo
[root@localhost ~]# nmcli
end0: ...

ttyUSB2: connecting (prepare) to wwan
        "Qualcomm SimTech SIM7080"
        gsm (option, cdc_ether), hw

lo: ...

The wwan connection is perpetually in connecting state.

The modem works if I use pppd with provided chat and options files, but I'd much rather get it to work with ModemManager and NetworkManager.

[root@localhost ~]# cat /etc/ppp/peers/sim7080option
/dev/ttyUSB3
3686400
nocrtscts
noauth
connect '/usr/sbin/chat -v -s -f /etc/ppp/sim7080-chat.dat'
disconnect '/usr/sbin/chat -e -v "" +++ath'
debug
ipcp-accept-local
ipcp-accept-remote
usepeerdns
noipdefault
defaultroute
lcp-echo-failure 3
lcp-echo-interval 2

[root@localhost ~]# cat /etc/ppp/sim7080-chat.dat
ABORT 'NO CARRIER'
ABORT 'NO DIALTONE'
ABORT 'ERROR'
ABORT 'NO ANSWER'
ABORT 'BUSY'
TIMEOUT 30
'' AT
OK ATE1
OK AT+CGDCONT=1,"IP"
OK ATD*99#
CONNECT ''

From looking at the mm debug logs, I noticed that

• mm uses ATD*99***3# whereas pppd uses ATD*99#
• a slightly different context "IPV4V6","internet","::",0,0,0 compared to the pppd version
• the ATD*99***3# command on ttyUSB3 never responds

I've tried switching ECM off and back on to see if it makes a difference - it doesn't.