Huawei ME909s-120 modem goes offline and disappears

[Bruno Vetter]

> Would you be able to draft a MM patch doing that?

Well-l-l...

I like to be challenged. Last time I coded in C is 20 years ago and I never contributed to open source. I might check out the sources and try to understand some basics over the next weeks, but cannot promise anything.

Apart from that: I had reproduced the issue with disappearing modem about 10 times now. I was always able to recover by issuing

systemctl restart ModemManager.service

and everything worked fine. I also had the impression that the primary port had somehow recovered by then.

One more question:
I found the following in the Huawei doc. When you talk about primary/secondary port, are we actually talking about Modem port/Uart port? Are they exchangeable?

...
The ME909s provides four ports to interact with its host:
 MODEM port: simulated using USB, for AT command interaction and establishing data connection.
Port name: HUAWEI Mobile Connect-3G Modem
 PCUI port: simulated using USB, for AT command interaction only.
Port name: HUAWEI Mobile Connect-3G PCUI Interface
 UART port: physical serial port, for AT command interaction and establishing data connection.
 ECM port: simulated using USB, for establishing communication connection. Port name: CDC Ethernet Control Model (ECM)
The ME909s also provides a port for debugging:
 DIAG port: simulated using USB, for DIAG (diagnostic) command interaction (mainly used to debug modules at present).
________________________________
Von: Aleksander Morgado <aleksander at aleksander.es>
Gesendet: Wednesday, December 18, 2019 6:54:20 PM
An: Bruno Vetter <bruno.vetter at outlook.com>
Cc: modemmanager-devel at lists.freedesktop.org <modemmanager-devel at lists.freedesktop.org>
Betreff: Re: Huawei ME909s-120 modem goes offline and disappears

> > No idea what else to do to solve this I'm afraid... :/ Maybe we could
> > extend the logic and add some automatic recovery mechanism to reset
> > the modem using the secondary port if we end up seeing that the
> > primary port is stuck like that? That wouldn't be ideal, but I assume
> > it's better to have one modem reset than having MM flag the modem as
> > failed.
>
> I am afraid I cannot give a suggestion here. I am just an MM user. Could you offer some advice for me how to work around the issue?
> We are dealing with a fleet of edge devices with a GSM only connection. So it is crucial for them to recover after such an issue.
> I could implement a watchdog service that detects the issue and resolves it. The question is how to detect and how to resolve.
> Without any further knowledge I could:
>
> Detect the issue by frequently executing mmcli -L to see if the modem has disappeared
> Resolve it by restarting the ModemManager service.
>
> Does that sound reasonable? If there is a more elegant way to do it please let me know.
>

I assume the issue is "solved" by restarting ModemManager just because
we end up using the previously secondary TTY as primary, but if that
gets also stuck, you may end up with the device completely stuck.

A better approach would be to detect that the primary control port is
stuck, and if there is a valid secondary port, try to run a modem
reset automatically using that secondary port. Would you be able to
draft a MM patch doing that?

--
Aleksander
https://eur04.safelinks.protection.outlook.com/?url=https%3A%2F%2Faleksander.es&data=02%7C01%7C%7Cc1433d0f8b96445ac06c08d783e35622%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637122884726105702&sdata=HcaGfa2b4QYiUTczqamkP%2FUuiYStD5rThv6JFaYjbh4%3D&reserved=0
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