Sierra EM7455 not recognized

[Bjørn Mork]

Tomek Mańko <jaennirin at gmail.com> writes:

> So my workplace bought some Lenovos L460 which are supposed to have Sierra
> Wireless EM7455 modems built-in (and indeed it does have a sim slot on the
> right side), but neither `lsusub` nor `usb-devices` seem to report any device
> with VID/PID 1199:9079 this modem is supposed to have. Manually `modprobe`ing
> WWAN-related drivers like `wcserial`, `cdc_wdm` or `cdc_mbim` doesn't cause any
>  new device to be recognised (I have no `/dev/cdc-wdm`, `/dev/ttyACM` nor
>  `/dev/ttyUSB` files and `dmesg` only reports the module loading message).

I can think of only 3 explanations:
 1) no modem installed
 2) modem is powered off by the BIOS
 3) modem does show up, but with a different VID/PID

I am not sure how Lenovo connects stuff nowadays, but wrt 2) you should
check the status of any radio kill switch.  "rfkill list" gives you the
list of supported hardware and software switches and their current
state.

As for 3), make sure that there is no unknown devices showing up.  You
should be able to figure out what they all are (hubs, camera, bluetooth,
fingerprint reader, etc). In theory your Lenovo EM7455 should only show
up as 1199:9079 (or possibly 1199:9078 if in bootloader mode), but maybe
you got some other modem? You cannot always trust what you're told by
resellers, unfortunately. And Lenovo provides a choice of different
modems AFAIK.

Wrt 1), the only way to make sure is to open up the laptop and see for
yourself.  This is usually pretty easy with Lenovo laptops.  If you
Google around you'll probably find the hardware maintenance manual,
telling you exactly where to find the modem m.2 socket.

Or you could just check the state in the Windows installation, if you
have one?


Bjørn