Some questions about qmi/wwan

[Robert Jones]

Hello Aleksander,

> You can connect them separately to e.g. different APNs, and have
> host-side routing rules for the different connections. That's at least
> one good use case.

That makes sense, thanks for the info.

I had a slight hiccup getting the raw-ip device to connect properly
with dhclient using the aforementioned commands, but realized I needed
to run 'qmicli --wda-set-data-format="802-3" ' before running the
qmi-network script. Worked like a charm after that.

On Thu, Aug 31, 2017 at 10:57 PM, Aleksander Morgado
<aleksander at aleksander.es> wrote:
>>> 2014-07-27 14:06 GMT+02:00 Aleksander Morgado <aleksander at aleksander.es>:
>>> > On Fri, Jul 25, 2014 at 9:00 PM, Dan Williams <dcbw at redhat.com> wrote:
>>> > - Once the kernel module is loaded, I get two /dev/cdc-wdm devices (0
>>> and
>>> >> 1). What are those for? The one that seems to be working with qmicli is
>>> >> /dev/cdc-wdm1. I also get two network interfaces, wwp0s20u6 and
>>> >> wwp0s20u6i3, the second one is the one that I can use dhcp client with
>>> and
>>> >> get an IP. Which is the purpose of the other one?
>>> >
>>> > I'll leave that to Bjorn and Aleksander, but on some devices there is a
>>> > second non-operative QMI configuration.  Could be a firmware quirk.
>>>
>>> Newer Sierra modems like the MC73XX series will expose two pairs of
>>> /dev/cdc-wdm (QMI) and wwan ports (usb interfaces 8 and 10). If you
>>> try to play with both you'll likely see that both reply to QMI but
>>> only one of the pairs gets correctly connected...
>>>
>>> The thing is that one pair comes by default with 802.3 ethernet frames
>>> configuration in the wwan interface, which is the one that the
>>> qmi_wwan kernel driver expects. The other pair comes with raw-ip
>>> packet configuration in the wwan interface, so you won't be able to
>>> use that pair directly with the qmi_wwan driver, *unless* you request
>>> to change that via e.g. qmicli
>>> --device-open-net="net-802-3|net-no-qos-header" or qmicli
>>> --wda-set-data-format="802-3". ModemManager does the device-open-net
>>> setup itself, so it can use both pairs directly.
>>
>> I've been asked what the difference is between these two /dev/cdc-wdm*
>> devices and even after reading this thread I'm still a bit confused.
>> The impression I get is that there is in fact no practical difference
>> between these two exposed channels/devices other than their default
>> (raw-ip vs 802-3) configuration.
>>
>
> I believe that's right.
>
>> If there is no difference besides that, what is the purpose of these
>> two separate channels as far as a developer/end user is concerned?
>>
>
> You can connect them separately to e.g. different APNs, and have
> host-side routing rules for the different connections. That's at least
> one good use case.
>
> --
> Aleksander
> https://aleksander.es



-- 
Robert Jones - Software Engineer
Gateworks Corporation - http://www.gateworks.com/
3026 S. Higuera St. San Luis Obispo CA 93401
805-781-2000