Restrict modem (EC21) one of 3G or 4G - ModemManager 1.10.0 (Debian Buster)

[Brendan Simon (eTRIX)]

On 18/08/2020 6:27 pm, Aleksander Morgado wrote:
> Hey,
>
>>>> I'm using a Quectel EC21 modem on a Debian Buster Linux system (using modemmanager 1.10.0).
>>>>
>>> Please note, MM 1.10.0 is a very very old release, no longer
>>> supported, and it's not even the last one inthe 1.10.x series...
>> Fair enough, but 1.10.0 is comes with Debian Buster, which is the latest
>> Stable release of Debian.  However there is a backport of 1.14, from the
>> Unstable (next release) distro, for Buster.
>>
> 1.10.0 was released in 2019-01-17, and after that there have been 4
> new updates in the 1.10.x series (1.10.2 on 2019-06-10, 1.10.4 on
> 2019-07-04, 1.10.6 on 2019-09-12, 1.10.8 on 2019-10-30. Then we have
> had the whole 1.12.x series up and running (7 releases); 1.12.0 was
> released on 2019-11-06 and the last 1.12.12 was released on
> 2020-06-23. 1.14.0 was released on 2020-06-23. You should probably
> poke Debian Buster packagers of ModemManager... they are 12 releases
> late in their latest stable release ;)

I guess it's a policy thing with Debian, where they choose stability 
over the latest and greatest, once a new distro is released.  All new 
development goes into the unstable distro, with backports from unstable 
to stable when necessary.

Since they have a backport for mm 1.14 I can't be critical of Debian 
being out of date (and I'm someone who tends to be lured by the latest 
and greatest shiny things ;-) )

>>> This may be a known issue with QMI modems where the internal network
>>> registration attempt is done with "QMI NAS Register In Network"; this
>>> command not only registers in network, it also makes the access tech
>>> preference fallback to "any", and MM doesn't consider that in its API.
>>>
>>> There is a recent patch to avoid this, by avoiding the use of "NAS
>>> Register in Network" and use "NAS Set System Selection Preference"
>>> instead: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/commit/c70b3557184fdf1472ff0cb36e9fd937cc7f9024
>>>
>>> That patch is not yet in any release, though, not even in 1.14.0. I'll
>>> backport it to the 1.14.x branch so that it gets into 1.14.2.
>>>
>>> You can confirm that this issue is happening to you by running this
>>> command once the tech went back to the one you didn't want:
>>> $ qmicli -d /dev/cdc-wdm0 -p --nas-get-system-selection-preference
>> Here is the output.
>>
>> # qmicli -d /dev/cdc-wdm0 -p --nas-get-system-selection-preference
>> [/dev/cdc-wdm0] Successfully got system selection preference
>>           Emergency mode: 'no'
>>           Mode preference: 'umts, lte'
>>           Band preference: 'wcdma-2100, wcdma-850-us'
>>           LTE band preference: '1, 3, 5, 7, 28'
>>           TD-SCDMA band preference: '(null)'
>>           Roaming preference: 'any'
>>           Network selection preference: 'automatic'
>>           Service domain preference: 'cs-ps'
>>           GSM/WCDMA acquisition order preference: 'wcdma'
>>           Acquisition order preference: lte, umts, gsm, td-scdma,
>> cdma-1x, cdma-1xevdo
>>
>> What are the key indicators that confirm the issue?
>>           Network selection preference: 'automatic'???
>>           Acquisition order preference: lte, umts, gsm, td-scdma,
>> cdma-1x, cdma-1xevdo???
>>
> Mode Preference (umts + lte) already tells you that the setting was
> reseted (assuming you requested 3G-only).
> The SSSP patch in network registration will very very likely solve
> your problems.

ok.  I will attempt one of the following.
- try to apply the patch to debian buster sources (1.10.0) and rebuild a 
new package.
- try to apply the patch to debian buster backport sources (1.14.0) and 
rebuild a new package.
- wait for a 1.14.2 release and poke the debian backport maintainer to 
generate a new release.

Thanks, Brendan.