Feature phone with 3G modem capability used to work under 1.18 but no longer works under 1.20

[Alex Villacís Lasso]

El 3/3/24 a las 03:14, Aleksander Morgado escribió:
> Hey Alex,
>
> On Mon, Feb 19, 2024 at 2:31 AM Alex Villacís Lasso
> <a_villacis at palosanto.com> wrote:
>> El 16/2/24 a las 17:48, Alex Villacís Lasso escribió:
>>> I have this old phone, a Samsung E3210B pre-Android feature phone that
>>> I wish to use as a fallback option when (more frequently than I would
>>> like) my broadband internet service goes down. When using ModemManager
>>> 1.18.x, I could plug in this phone, and it would expose a single
>>> /dev/ttyACM0 port for all interactions including AT commands and PPP.
>>> Then ModemManager could connect to the internet using the port as
>>> normal, using the "generic" plugin. Now, using ModemManager 1.20.6
>>> under Fedora 39, the same phone fails (with a timeout) to establish a
>>> connection using ModemManager. However, it does setup a proper
>>> connection using wvdial from the command line, even under Fedora 39.
>>>
>>> After a while, I managed to perform a git bisect on the code, and
>>> pinpointed the first commit that breaks my phone, to commit
>>> 213cd81b3ade35024e2d702e2726273f00344185 "iface-modem-simple: wait for
>>> packet service 'attach' state in ConnectionStep". However, I am now at
>>> a bit of a loss at understanding the supposed purpose of this commit.
>>> Full details are at this bug report:
>>>
>>> https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/743
>>>
>>> The patch no longer cleanly reverts under 1.20.x, so I cannot just rip
>>> it off...
>>>
>> I have updated the bug report with a new discovery: ModemManager 1.20
>> will dial into the phone immediately, if I first manually select some
>> phone feature that requires Internet access (such as Google Search),
>> then click OK in the little dialog that ask to connect to the Internet.
>> However, this manual interaction with the phone should be unnecessary,
>> because it was not needed with ModemManager 1.18 and is also not needed
>> when using the phone through wvdial.
>>
>> I need a way to tell ModemManager when using this particular phone to
>> connect, to IGNORE the "searching" status of the GPRS registration and
>> dial anyway, since the GPRS will be enabled by the very act of dialing
>> the Internet access sequence. Is there any existing way to do that?
>>
> I replied at the issue, I believe your problem would be solved with MM
> 1.22 and https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/commit/179a800ab64b28f5437c3d06056640f702e68aa5.
> You may still experience some delay to connect, because MM will first
> wait some seconds for the attach state to come up automatically, and
> only otherwise try to send the operation to activate it.
>
> Either way, it looks like your device needs a much more relaxed logic
> in this regard, so fully ignoring the packet service attach state
> would be a better option probably.
>

I have updated the bug report. With ModemManager 1.22 on Fedora 40, the 
phone is not even recognized as a valid modem, even though wvdial 
continues to work with it. On a separate machine using Debian Testing 
(Trixie) with the same minor version (1.22) the problem also exists.