[OpenWrt-Devel] [PATCH uqmi] nas: add --get-plmn

[Martin Schiller]

Ping.

I still want to fix the existing problems in the qmi protohandler.

Therefore, this feature needs to be integrated into uqmi.

Martin

On 2019-08-29 10:35, Bjørn Mork wrote:
> Martin Schiller <ms at dev.tdt.de> writes:
> 
>> On 2019-08-26 21:12, Sami Olmari wrote:
>>> I think the ideology behind proto handler there is to "do whatever
>>> told" despite of what the state is currently,
>>> maybe there is a reason for such behaviour (searches some stuff from
>>> network etc).
>> 
>> There exist 2 problems in the qmi proto handler:
>> 
>> 1. Setting the plmn to 'auto' will implicitly lead to a (delayed)
>> network re-registration, which could further lead to some timing
>> related issues in the qmi proto handler.
>> Let me explain this in more detail:
>> After successfully calling the uqmi --set-plmn (auto) command it takes
>> up to 5 (or maybe even more) seconds until the modem detaches from
>> network
>> and start searching for new registration.
>> 
>> In the meantime the proto handler goes through the next steps
>> ("Waiting for
>> network registration", "Start network $interface" etc.).
>> 
>> I hope you can see were this leads to.
>> 
>> This is really a problem in Roaming scenarios, where to provider maybe
>> is
>> switched after the re-registration.
> 
> 
> FWIW, I also believe this is a real problem.
> 
> The modem firmware isn't always smart.  It will "do whatever told", 
> even
> if it is a completely unnecessary de-registration, network scan and
> re-registration.
> 
> We can be smarter than that.  We should avoid changing any persistent
> (in modem nvram) setting related to network registration, unless
> absolutely necessary.
> 
>> 2. The plmn setting is permanently saved in the wwan modem:
>> This leads to the problem, that if you switch back from manual plmn
>> selection
>> to auto mode you have to set it explicitly to 'auto'.
> 
> Yes, the current handler will use whatever is stored in the modem 
> unless
> 'plmn' is explictly set.  This is very confusing if you set 'plmn'
> temporarily, whether it is for roaming or just experimenting. Users 
> will
> rightfully assume that adding and then removing 'plmn' means 'no
> change'.
> 
> Everything in the qmi proto handler should take into account that
> settings might be stored in the modem nvram.  Optional settings need an
> explicit default, and should always be verified against the value 
> stored
> in the modem.
> 
> I believe the 'plmn' default should be 'auto'. But we can only do that
> if we first add the logic to verify the current setting and avoid any
> unnecessary 'uqmi --set-plmn' commands.
> 
> 
> 
> Bjørn


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