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

[Bjørn Mork]

Sergey Ryazanov <ryazanov.s.a at gmail.com> writes:

> On Sun, Dec 5, 2021 at 3:32 PM Bjørn Mork <bjorn at mork.no> wrote:
>> Sergey Ryazanov <ryazanov.s.a at gmail.com> writes:
>>> 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 agree that this is rare.  But I'm pretty sure it can happen.
>>
>> A more common case is that the modem picks some arbitrary previously
>> used APN, e.g. profile #1. This will often be fine. But it can be really
>> annoying when it isn't. For example becasue that profile was configured
>> as IPv4 only and you want a dual-stack connection.
>
> Should not a modem reestablish a bearer as soon as a user provides a
> new APN along with the connect QMI command?

I don't know what a modem should do.  I only know what I've observed: If
a modem is attached to a network using an IPv4 only default bearer, then
you cannot connect a dual stack bearer.  You can connect it, but you'll
only get the IPv4 part of the session up.  And connecting an IPv6 only
APN is impossible in this case.

>> So flight mode will sometimes be necessary when changing APN.
>
> Just to make it clear. Should switching to the airplane mode be a part
> of connection establishing procedure (i.e. qmi.sh script)? Or would it
> be enough to have the mode switching command in the uqmi utility? So a
> user will be able to manually toggle the airplane mode during the APN
> reconfiguration.

I'm not able to agree with myself here :-)

On one hand, I believe toggling airplane mode after we know the initial
APN would make this more robust.  On the other hand, I fear that kind of
automatic stuff.

Better leave if for the user as a manual toggle, I guess.

>> Just don't ever force it. We don't want to lose the ability to connect
>> to more than one APN (although this probably isn't supported in uqmi yet
>> since you can't setup QMAP).
>
> Do not understand this phrase. How can the airplane mode break a
> multi-bearer setup?

I don't know if this was the plan or not.  But I feared that someone got
the idea that you could force airplane mode whenever a new APN is
configured.  This would obviously break existing connections.

> BTW, when you are talking about QMAP, did you mean utilizing the QMAP
> demux module from the kernel as it is or implementing the WWAN
> subsystem ops for the qmi_wwan module. In other words, did you mean
> protocol or implementation?

I was talking about the (lack of) muxing setup support in uqmi.  There
is no way to tell the modem firmware how the different channels are
supposed to be connected.


Bjørn