MC7455/EM7455 dependencies and protocols

[Bjørn Mork]

[starting a new thread with the answers...]

Tim Harvey <tharvey at gateworks.com> writes:

> Hi Bjørn,
>
> Can you tell me more about how you got this modem working? I'm trying
> to understand:
> - what Linux drivers are required and do you have to inject new_id's
> vis sysfs to get them to probe (none of the drivers seem to recognize
> the 0x1199:0x9079 by default)

Depending on the modem firmware configuration you may need cdc_mbim,
qmi_wwan and qcserial.

The 9079 PID is Lenovo specific, and AFAIK always in MBIM mode by
default. The cdc_mbim driver matches on class attributes, so there is no
need for any device specific IDs.

Wrt non-default configurations, both the 1199:9071 (Sierra default) and
1199:9079 (Lenovo ID) were added to the qcserial and qmi_wwan drivers in
Linux v4.5.

> - what managment and communication dev nodes should be created

Depends on modem firmware configuration.  Typically one or more
/dev/cdc-wdmX nodes, one or more wwanY netdevs and zero or more
/dev/ttyUSBz nodes.

> - what libqmi version is required

The latest.

> - what the difference is between mbim and qmi

Different protocols for management and data framing.  No need to worry
about that.  The drivers and ModemManager will figure it out.

But if you do want to worry, then Google has lots of interesting info :)

> - what the firmware dependencies are, how to tell what firmware I have
> on them, and how to update if required

ModemManager will tell you the firmware revision regardless of protocols
and drivers in use.  AFAIK, updating is not required for any
production MC7455/EM7455.

> I've got an MC7455 as well as an EM7455 on hand to test with but
> haven't gotten either to be recognized by any of the Linux drivers (at
> least in 4.4).

You'll need Linux v4.5 or later for QMI on these modems.

And you'll probably need v4.7 or later for MBIM. Or one of the stable
kernels with a backport of c086e7096170 ("cdc_ncm: workaround for EM7455
"silent" data interface"), for example v4.4.16 or later.



Bjørn