Sorry about being much too late into this discussion.  I'm not having
the bandwidth to read netdev anymore, and just stumbled across this now.

Andrew Lunn [off-list ref] writes:

So, this is what all the Ethernet nonsense is all about. You have a
session ID you need to somehow represent to user space. And you
decided to use VLANs. But to use VLANs, you need an Ethernet
header. So you added a bogus Ethernet header.

Actually, the original reasoning was the other way around.

The bogus ethernet header was added because I had seen the 3G modem
vendors do that for a few years already, in the modem firmware.  And I
didn't think enough about it to realize that it was a really bad idea,
or even that it was something I could change.  Or should change.

I cannot blame the MBIM sesison to VLAN mapping idea on anyone else.  As
far as I can remember, that was just something that popped up in my head
while working on the cdc_mbim driver. But it came as a consequence of
already having the bogus ethernet header.  And I didn't really
understand that I could define a new wwan subsystem with new device
types. I thought I had to use whatever was there already.

I was young and stupid. Now I'm not that young anymore ;-)

Never ever imagined that this would be replicated in another driver,
though.  That doesn't really make much sense.  We have learned by now,
haven't we?  This subject has been discussed a few times in the past,
and Johannes summary is my understanding as well:
"I don't think anyone likes that"

The DSS mapping sucks even more that the IPS mapping, BTW.  I don't
think there are any real users?  Not that I know of, at least.  DSS is
much better implmeneted as some per-session character device, as
requested by numerous people for years.  Sorry for not listening. Looks
like it is too late now.

Is any of this VLAN stuff required by MBIM?

No.  It's my fault and mine alone.

I suggest you throw away the pretence this is an Ethernet device. It
is not.

I completely agree.  I wish I had gone for simple raw-ip devices both in
the qmi_wwan and cdc_mbim.  But qmi_wwan got them later, so there is
already support for such things in wwan userspace.


Bjørn