[uqmi] dms: add --get-operating-mode

[Sergey Ryazanov]

CC Piotr and Matti to draw some more attention to this case.

On Sun, Dec 5, 2021 at 2:19 AM Henrik Ginstmark <henrik at ginstmark.se> wrote:
> Den lör 4 dec. 2021 kl 23:19 skrev Sergey Ryazanov <ryazanov.s.a at gmail.com>:
>> On Sat, Dec 4, 2021 at 6:22 PM Henrik Ginstmark <henrik at ginstmark.se> wrote:
>>> This command make it possible to query if the modem is in flight mode or not.
>>>
>>> If you need to change your APN setting it should be done during flight mode on.
>>
>> Just curious, is this true for any Qualcomm based mode or only for a
>> specific model?
>
> When an LTE terminal is powered on it needs a valid APN to be able to
> register to the
> network. Some cellular operators allow an "empty" APN and then set a default APN
> to the terminal.
> The most optimal way to power on an LTE terminal would be with flight mode on,
> check that the correct APN is configured and then set flight mode off.
> This is for all LTE terminals.

Sounds stranger. In the OpenWrt at the moment, APN passed to a modem
during the data connection establishment stage. A long time after the
modem will be registered with a cell network. uqmi.sh script even has
a special busy loop that waits the modem registration procedure
completion to avoid data connection establishing failure.

>From the 3GPP specification point of view, a UE (modem) has at least
three options during the initial network registration procedure:
* request the immediate default connection establishing with a
specific P-GW (APN) via a long and tricky procedure;
* request the immediate default connection establishing without an
explicit APN, then MME should use a default one P-GW (APN);
* do not establish a data connection immediately.

I am, as an occasional user of an LTE modem, never faced a case when
the modem is unable to register with a network due to an unconfigured
APN. The most prominent fact is that no one else ever faced such case
for a 7 years of the uqmi existence. It looks like you either ran into
a very special operator, or you have a buggy modem that is recovered
via the airplane mode. It is also possible that I do not fully
understand your case.

I am not against this patch, I am just curious about the described
situation with a strict APN requirement.

> I have a local uqmi version with commands for checking and modifying
> the APN settings.
>
>>> To make it possible to automate change of APN setting --get-operating-mode is
>>> needed.
>>>
>>> Signed-off-by: Henrik Ginstmark <henrik at ginstmark.se>

-- 
Sergey