Multiple PDN with libqmi/ModemManager?

[Bjørn Mork]

"Martin Anderseck" <Martin.Anderseck at ni.com> writes:

>> The MC7710 can be configured to expose 3 QMI ports.  You can find
>> instructions on how to do that hidden in Sierra Wireless' excellent
>> AT command documentation, which I believe now is available to anyone
>> registering on http://developer.sierrawireless.com/
>
> Found it, thank you for indirectly pointing me at this. Currently I don't have multiple PDNs/bearers available for testing but next week I'll continue working on this. 
>
>> Now I never made the 3rd port work, and quite frankly I believe there is
>> a firmware bug preventing that.  The qmi_wwan driver will ignore it for
>> this reason.  But the 2 first ports work fine and can be used for
>> simultaneous packet network connections.
>
> I guess we're talking about config #7, right? I only have two ports working, too, so it seems I hit the correct one :-)

Yes, that's the one.

You also have a combination of that config + MBIM, using multiple USB
configurations to select between QMI and MBIM.  But the switching is a
bit buggy.  The modem will actually sense which protocol you talk, and
lock to that independently of the USB descriptors.  So you can end up
with a QMI speaking modem looking like an MBIM one.  Or vice versa.

And switching descriptors from MBIM to QMI after a while in MBIM mode (I
do not know the exact trigger here - only that the bug can be prevented
by switching immediately after booting the modem), results in a
completely non-functional QMI mode.  You won't notice until you fire up
a DHCP client after connecting.  Then the modem starts flooding the host
with zero length packets.  This used to kill the host, but we now have
some protection against it in usbnet.  You will still notice that your
PC gets hot after a while, doing absolutely nothing. So don't do this
with a MC7710.  If your modem is set up for dual MBIM/QMI mode and you
want to use it in QMI mode, then use a udev rule to switch (it will
default to MBIM because proper classes are preferred over vendor
specific).

>> I was hoping the MBIM version of the firmware would expose the same
>> capability using MBIM IP session multiplexing, but the firmware I've got
>> so far does not seem to do this.  Still hoping that will improve in the
>> future.  The MBIM firmware still support the 3 QMI ports when configured
>> for QMI operation.
>
> I didn't test it yet but would you consider MBIM as usable? I'm using
> firmware 03.05.19.04ap btw. and I can confirm that there is only one
> MBIM port available in the supported profiles. 

Yes, MBIM is certainly usable. That's what I use, with that same
firmware version.  Don't know if there is anything newer available?
There are certainly enough bugs in that version to warrant a new
release, but that one seems to be the one distributed to all the laptop
vendors...

You do currently lose some functionality with MBIM on the MC7710, like
the multiple net ports, the nice Sierra AT command interface, and the
GPS. Or... that's possibly still accessible using the QMI-in-MBIM
interface? Anyway, I guess most people will be more satisfied with the
QMI mode at the moment, because the support is more complete both on the
firmware side and on the userspace side.  Still, for plain network
access then MBIM is working nicely.  And you can help test libmbim :)


Bjørn