DSS usage

Aleksander Morgado aleksander at aleksander.es
Fri May 9 01:25:49 PDT 2014

On Fri, May 9, 2014 at 9:41 AM, Bjørn Mork <bjorn at mork.no> wrote:
>> It's not like we can make the driver just create a character device and
>> make it immediately available for any legacy application written for a
>> serial port. MBIM DSS sessions are not just "there", like for example a
>> USB serial function. Something has to manage the session, and this
>> something should know what type of data the stream contains.  This
>> "something" can then just as well set up the necessary data
>> transformation for any legacy application it wants to support.
>> For example, if you want to support NMEA over DSS using gpsd, then you
>> will create a userspace application which
>>  - starts the appropriate DSS session
>>  - creates the matching VLAN
>>  - proxies the VLAN to a pty, adding and stripping ethernet headers
>>  - adds the pty to the list of gpsd devices
>> I believe it would make sense for libmbim to provide utility functions
>> taking care of the first three.
> If I were more of a programmer, then I would of course have worked on a
> real implementation for libmbim.  The truth is that I don't have a clue
> where I would start doing that.  So therefore, this proof-of-concept is
> all you get for now.

Kind of like this approach. So, if I'm not mistaken, a single
user-space app can take care of providing ptys for the different DSS
sessions managed in the system, by R/W packets from/to the network
interface and doing the forwarding to/from the corresponding PTY,
without any VLAN interfaceinvolved. This can likely be integrated in
the mbim-proxy setup that Greg wrote, which I still need to review;
i.e. whenever the mbim-proxy receives a DSS channel creation request,
it could also transparently create a new pty for it. We could then
provide an internal API between mbim-proxy and libmbim to report the
pty path,  or otherwise, let libqmi build itself the path based on the
DSS channel number or something. Is that the general approach you're
suggesting? Or did you have some other thing in mind?


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