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

[Aleksander Morgado]

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?
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