Sierra Wireless EM7455

[Bjørn Mork]

Andreas Fett <andreas.fett at secunet.com> writes:

> Hi list,
>
> I'm dealing with a Sierra Wireless EM7455 as used in Lenovos T460s.
>
> For this modem the mbim driver attaches and works well (ie the sim can
> be unlocked) until I try to connect. It then fails during a "set
> radio-state" command.

Lenovo has turned on the "FCC_AUTH" feature on their EM7455 modules.
This disables the radio until the modem has received a magic command.
MM has support for doing this for QMI, but not yet for MBIM.  We know
how it can be done, though.  See the recent discussion at:
https://lists.freedesktop.org/archives/libmbim-devel/2016-April/000703.html

> Kernel Version is 4.5, I'm somewhat confused however by two recent
> commits in this kernel version which place the USB IDs of this device in
> the qmi_wwan and qcserial drivers both of which do not attach.

No need for those commits (or even a recent kernel) for MBIM mode.
Those patches were submitted just in case someone configures their
Lenovo OEM'd EM7455 for QMI (and/or serial functions).

A quick note before anyone tries that:

I don't actually know whether QMI is supported by the EM7455 in a Lenovo
laptop.  I assume the modem firmware has the same support as in other
versions, but I do not know how the Lenovo BIOS will react to such a
change.  I assume Lenovo still does USB ID whitelisting, and that the
only accepted version of the EM7455 is the one with PIDs 9078/9079
(boot/appl). They might accept changing the modem to QMI mode if you
keep these PIDs.  But testing that is risky.  You should not try to do
so without being prepared to physically remove the modem and connect it
to another (non-Lenovo) host to change it back.  Which requires an m.2
connector of some sort.


Bjørn