Random QMI port probe failures after ed13e053cd42 ("port-probe: fix custom init probing not having open AT port")

[Aleksander Morgado]

Hey,

On Sun, Dec 22, 2024 at 6:49 PM Aleksander Morgado <
aleksander.morgado at gmail.com> wrote:

>
>
> On Sun, Dec 22, 2024 at 6:37 PM Aleksander Morgado <
> aleksander.morgado at gmail.com> wrote:
>
>> Hey,
>>
>>
>>> > > After updating to the latest main (at eda130f3bf1c), in our team
>>> > > we've noticed, that in our CI, that QMI port sometimes fails to
>>> > > probe,
>>> > > with Telit LE910C4-WWXD. The result is the modem having only AT
>>> > > ports
>>> > > available, thus falling back to using PPP for the data connection.
>>> >
>>> > Well that's not awesome; I'll dig into it. If you figure out anything
>>> > too, let me know.
>>> >
>>>
>>> When this happens, does MM attempt to probe the port as AT before
>>> trying QMI?
>>>
>>>
>> With the changes in that referenced commit, it looks like
>> serial_probe_step() may be running serial_open_at() also for the QMI and
>> MBIM ports, which is not right, as that would create a new MMSerialPort in
>> ctx->serial.
>>
>> The serial_probe_step() (ideally renamed as probe_step() to make it
>> clearer that it is not serial-specific) should not run any serial-specific
>> operation (e.g. CUSTOM_INIT, AT_OPEN_PORT, ....) for ports that do not
>> require any AT or QCDM probing.
>>
>> WDYT?
>>
>
> The issue can be reproduced with modems for which the corresponding plugin
> has "custom_init" configured, e.g. Telit or Cinterion:
>
> ModemManager[4112]: <dbg> [1734889629.161510] [cdc-wdm0/probe] no
> AT/QCDM/QMI probing in possible MBIM port
> ModemManager[4112]: <dbg> [1734889629.162057] [cdc-wdm0/probe] port is not
> AT-capable
> ModemManager[4112]: <dbg> [1734889629.162867] [cdc-wdm0/probe] port is not
> QCDM-capable
> ModemManager[4112]: <dbg> [1734889629.163621] [cdc-wdm0/probe] port is not
> QMI-capable
> ModemManager[4112]: <dbg> [1734889629.164981] [cdc-wdm0/probe] launching
> port probing: 'mbim'
> ModemManager[4112]: <msg> [1734889629.166516] [cdc-wdm0/probe] probe step:
> start
> ModemManager[4112]: <msg> [1734889629.166988] [cdc-wdm0/probe] probe step:
> custom init open port
>

I tried to fix this with
https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/1273

Let us know if this solves the problem completely or not.
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