problem with Sierra MC7750 (and a workaround)

[Tim Harvey]

> Heath Kehoe <heath at digitalartefacts.com> writes:
>
>> I was trying to get an MC7750-based USB modem working with libqmi. The
>> kernel modules sierra and qmi_wwan are loaded when the device is
>> connected; I can use qmi-network to start the data connection, and
>> everything seems to work except there's no data flow. No packets get
>> sent or received.
>>
>> Turns out the problem is that the modem needs to be explicitly told to
>> use QMI_CTL_DATA_LINK_PROTOCOL_802_3 via CtlSetDataFormat. And since
>> qmicli basically uses the default flags to qmi_device_open, libqmi
>> doesn't send a CtlSetDataFormat.
>>
>> As a quick-and-dirty workaround, I hacked qmicli.c to add
>> QMI_DEVICE_OPEN_FLAGS_NET_802_3 and
>> QMI_DEVICE_OPEN_FLAGS_NET_NO_QOS_HEADER to open_flags. With that
>> change, the MC7750 works.
>>
>> I was thinking I could extend qmicli.c to add a new option to be able
>> to set those flags. Something like:
>>
>>    --device-open-net=<mode> where mode is:
>>             "en"  : 802_3 + NO_QOS_HEADER
>>             "eq" : 802_3 + QOS_HEADER
>>             "rn" : RAW_IP + NO_QOS_HEADER
>>             "rq" : RAW_IP + QOS_HEADER
>>
>> If the option is not given, the behavior will be like it is now (no
>> flags, which means no CtlSetDataFormat is sent).
>>
>> Thoughts?
>
> Adding the option, indluding the ability to not send CtlSetDataFormat at
> all, seems like a very good idea to me.
>
> But I wonder if maybe the default should be set to "802_3 +
> NO_QOS_HEADER"? That's the only mode currently supported by the driver,
> and I don't see any immediate change coming up.  So this is most likely
> to just Make Stuff Work.  Unless there is some buggy device which barfs
> on this command, of course.  But I haven't heard of that yet, and as you
> note: MM will send this command on open.
>
>
> Bjørn

Did anything ever come of this idea?  It appears to me that this patch
is necessary for a 4G/LTE connection but not a CDMA-1X/EVDO
connection.

Thanks,

Tim