Sierra Wireless EM7455, MBIM connect

[Bjørn Mork]

Fabian Schörghofer <fabian.schoergi at gmail.com> writes:

> I have a Sierra Wireless EM7455. It is supposedly in MBIM mode, as the
> dmesg output shows a new /dev/cdc-wdm0 device, and wwan0 with mbim.
> The device is not from a Lenovo notebook. Firmware is
> SWI9X30C_02.08.02.00.
>
> I know that during this device is using rawip to transmit data, which
> only works on newer kernels, I got kernel 4.6.0 rc2 running.

Not really necessary for MBIM.  The EM7455 should work with any kernel
newer than v3.7.

> I tried to connect with the following commands:
>
> mbimcli -d /dev/cdc-wdm0 --register-automatic
> mbimcli -d /dev/cdc-wdm0 --connect=drei.at
>
> (no user/pw is required)
>
> But then I do not know if I am connected and how to assign the IP to wwan0.
> dhclient -i wwan0 is not working.

When using mbimcli, you need to be careful to manually open the MBIM
session once and keep it open for as long as you intend it to last. You
do this by adding "--no-close" to all commands but the last one, and
"--no-open=xxx" to all commands but the first one.

This is a little tedious, but the mbimcli is mostly a debugging utility...

The mbim-network script will do all the work for you.  Use it as a guide
if you don't want to use it directly.

I also recommend always using the MBIM proxy with these devices.  And
all others, really.  In my experience, opening and closing the
/dev/cdc-wdm0 device will sooner or later end up with the driver and
firmware coming "out of sync". Yes, I should fix that.

But use the proxy.  It saves you from worrying about this.

> I try to avoid using ModemManager or Networkmanager to connect, as I
> might not have those installed on the device I plan to use it.
> Nevertheless I tried connecting with:
>
> mmcli -m 1 --simple-connect="apn=drei.at,ip-type=ipv4"
>
> but no result either. Not sure about the ipv4 type, or if its just plain "ip".

ipv4 is correct.

"mmcli -m 1" should show you the number of the created bearer, and
"mmcli -b x" should show you all the gory bearer details, including ip
configuration.

> On some forums I heared that it is possible to switch the device to
> QMI, is this the better/more elegant way to connect the device, and
> how can the device be changed? Some AT-command?

Don't know if it should be considered better or not.  It's mostly just
different :)

You can switch by AT command, QMI command (also in MBIM) or writing to
NVRAM.  AT command is the only documented and supported method, AFAIK.
You can download the AT command docs from Sierra after registering.

The command in question is also mentioned in public.  E.g. here:
https://forum.sierrawireless.com/viewtopic.php?f=117&t=9266#p37082
(for anyone else reading this:  that command is currently only for the
EM/MC74xx series)

Note that the command is password protected for good reasons. But the
password is also "well known.  You can find it e.g. here:
https://whirlpool.net.au/wiki/sierra_advanced

The primary purpose of the password seems to be to protect the innocent.
It is possible to configure settings which do not work for you.  There
is always a way back, but it might require assistance....


Bjørn