Quectel EC25 & AT&T connection Catch-22

[Enrico Mioso]

On Fri, Apr 19, 2024 at 04:39:46PM +0000, Bruce Johnson wrote:
> I have a question about using both QMI and the serial interface with ModemManager.
> 
> I had little difficulty getting ModemManager's SimpleModem to connect to T-Mobile (USA) using a Quectel EG25-G, but we found that modem wasn't compatible with AT&T and/or a private APN used by one of our customers. We were advised to use the Quectel EC25, and after engaging both Quectel and AT&T, we were told that we need to insert the APN into the modem using an AT command, AT+CGDCONT=1,"IPV4V6","mcm.com.attz". I had to tweak the kernel config and the ModemManager build.
> 
> Mods:
> 
>   *   I built ModemManager 1.18.4 with --with-at-command-via-dbus.
>   *   In the kernel config, I added USB Serial Converter support -> USB driver for GSM and CDMA modems.
> 
> After I did this, the /dev/ttyUSB[1-4] files showed up, and I was able to issue AT commands using ModemManager, but while the modem would sort-of connect with SimpleModem's connect method -- I am getting a Bearer, and mmcli shows "connected" -- I receive no IP address information from the carrier. Port wwan0 is showing up as "ignored". (mmcli output below)
> 
> The Quectel docs also said to patch the kernel a certain way to allow use of serial and the QMI_WWAN driver, but wwan0 is still ignored.
> 
> Does anyone have any suggestions?
> 
> Thanks!
> 
> --
> Bruce Johnson
> Chantilly, Virginia
> USA

I will stand corrected in case - but...
I don't think you need AT commands via d-bus to do this, but giving the APN via QMI somehow, depending on the object or method you use to connect.
That said, you probably won't need qmi_wwan_q or whatever - the stock qmi_wwan driver from kernel, and "option" for serial should suffice.

For some reason you have wwan0 (gnored) in your output which doesn't sound right. I would try to look at it/fix it first.

Enrico



> 
> 
>   --------------------------------
>   General  |                 path: /org/freedesktop/ModemManager1/Modem/0
>            |            device id: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
>   --------------------------------
>   Hardware |         manufacturer: Quectel
>            |                model: EC25
>            |    firmware revision: EC25AFFAR07A14M4G
>            |            supported: gsm-umts, lte
>            |              current: gsm-umts, lte
>            |         equipment id: 359401089771197
>   --------------------------------
>   System   |               device: /sys/devices/pci0000:00/0000:00:15.0/usb1/1-4
>            |              drivers: option, qmi_wwan
>            |               plugin: quectel
>            |         primary port: ttyUSB3
>            |                ports: ttyUSB2 (gps), ttyUSB3 (at), ttyUSB4 (at), wwan0 (ignored)
>   --------------------------------
>   Status   |       unlock retries: sim-pin (3), sim-puk (10), sim-pin2 (3), sim-puk2 (10)
>            |                state: connected
>            |          power state: on
>            |          access tech: lte
>            |       signal quality: 60% (recent)
>   --------------------------------
>   Modes    |            supported: allowed: 2g, 3g, 4g; preferred: none
>            |              current: allowed: 2g, 3g, 4g; preferred: none
>   --------------------------------
>   IP       |            supported: ipv4, ipv6, ipv4v6
>   --------------------------------
>   3GPP     |                 imei: 3594010XXXXXXXX
>            |          operator id: 310410
>            |        operator name: AT&T
>            |         registration: home
>   --------------------------------
>   3GPP EPS | ue mode of operation: csps-2
>   --------------------------------
>   SIM      |     primary sim path: /org/freedesktop/ModemManager1/SIM/0
>   --------------------------------
>   Bearer   |                paths: /org/freedesktop/ModemManager1/Bearer/0
> 
>