Re: Linux MBIM

On Wed, 2012-07-18 at 16:17 -0700, Greg Suarez wrote:
> On Mon, Jul 16, 2012 at 12:28 AM, Bjørn Mork <bjorn mork no> wrote:
>         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 :-)
> I was on the same line of thinking but wasn't aware of the QMI driver.
> Could you point out its location to me?
>         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?  
> I ask because I've been assigned to either come up with a MBIM driver
> or help with an existing effort.

Ideally the control channel and ethernet (or Raw IP) bits get done in
the kernel drivers, while for the actual control protocol we have a
simple LGPL userspace library that apps like ModemManager can make use
of to talk over that control channel.  A lot like we've done for QMI,
DIAG, and WMC already.  Then we can just plug that code in like we've
done for all the other methods.

>         Do you know of any
>         device? Or planned device?  Where can I get one? :-)
> I should be getting a dev board sometime in the next few weeks.  I
> don't even know the manufacturer.
> Where can you get one?  no idea.
>         Bjørn
> Thanks,
> Greg
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