Some questions about qmi/wwan

[Aleksander Morgado]

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.

-- 
Aleksander
https://aleksander.es