Re: Linux MBIM

Aleksander Morgado <aleksander lanedo com> writes:

>> I was wondering if there's any effort going on to support MBIM devices
>> on Linux?
> No plans yet for ModemManager (see thread [1]). Is there any device
> out there which already supports that protocol?
> Cheers,
> [1]

If I understand this correctly, MBIM devices will combine CDC NCM with a
MBIM control channel in the exact same way QMI devices combine CDC ECM
with a QMI control channel.  That means that the driver support could be
done as simple as combining cdc_ncm with the cdc_wdm subdriver (either
in the existing cdc_ncm driver, or as a new separate driver reusing code
from cdc_ncm).

If this was done, then we would have the MBIM control channel exported
to userspace as a /dev/cdc-wdmX device, exactly like qmi_wwan exports
its QMI control channel.  Leaving MBIM control protocol implementation
for userspace make sense for the same reasons it made sense to leave QMI
implementation for userspace.  Boy, am I happy Marcel and others
convinced me to do that :-)

Hmm, I see now "The only difference is that instead of transporting
Ethernet frames, MBIM transports raw IP data streams".  So we definitely
need a new driver based on cdc_ncm.  Exporting and reusing a bit of
cdc_ncm would probably make most sense.  And it might also be necessary
to extend the cdc_wdm subdriver interface if the cdc_ncm driver need to
notifications, or if it needs to send any control messages after the
probe phase.  Don't know if it does.  Doesn't really look like it…

All this should still be a piece of cake to stitch together.  If there
had been any devices, that is. So, no, I don't know of any effort to
support MBIM on Linux.  There just isn't any need for it yet.  The basic
kernel driver support can be added in a few weeks if necessary.

See also the reply from Torgny Johansson in the thread Aleksander refer
to, pointing to this press release:

I am guessing here, but the whole MBIM thing looks like it was driven by
Ericsson, and it might just not happen when they have put it on hold.
Qualcomm are likely to be happy with their current QMI approach.  Not
sure what value they would see in replacing that with a new standardized
protocol, if they are going to be the only ones using the new protocol...
Others? Microsoft?  Yes, I guess they could drive this if they decided
that MBIM is the "RNDIS of wwan devices".  Maybe they will??

A question back to you, Greg:  Why do you ask?  Do you know of any
device? Or planned device?  Where can I get one? :-)


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