[Pkg-utopia-maintainers] Enabling MBIM in Debian

[Bjørn Mork]

Ben Hutchings <ben at decadent.org.uk> writes:

> Starting with linux version 3.8.2-1~experimental.1 we've included the
> new cdc_mbim driver for MBIM (Mobile Broadband Interface Model).
>
> Newer modems support both NCM or MBIM, but only one at a time, selected
> by the kernel drivers.  For compatibility with current userland, the
> kernel has been changed in version 3.8.5-1~experimental.1 to prefer NCM.
> Once your package has support for MBIM, you should enable it in the
> kernel by installing a uniquely named file in /lib/modprobe.d
> containing:
>
> options cdc_ncm prefer_mbim=Y

Just FYI: There is now a set of modems which claim to support a NCM/MBIM
backwards compatible function, but where we do not know how to use the
NCM variant. Or even if it is actually supportable at all - there is no
evidence that any other OS uses it.

The implication is that the 'prefer_mbim=Y' configuration shown above is
*required* to make these modems work in Jessie.  ModemManager will
otherwise fail to recognise and manage them.

The most common example of such a modem is the Sierra Wireless EM7345,
used by Lenovo in their current range of Thinkpad T and X series
laptops. These are popular enough to make me expect this problem to
become a FAQ once Jessie is out.

Unfortunately I did not anticipate this situation when adding the module
parameter in the first place.  I stupidly assumed that we would be able
to support both NCM and MBIM modes for all modems which claimed such
dual support. There is therefore no way to make a per-device setting of
this option in the 3.16 kernel.

Sorry about this mess... Suggestions on how to improve/fix it (both for
mainline and for the Jessie kernel) are appreciated.


Bjørn (who just stumbled into this while testing out the 3.16 kernel in
experimental)