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

[Aleksander Morgado]

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
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