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

[Alex Villacís Lasso]

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?