Re: [PATCH net-next 16/17] Documentation: networking: dsa: Add details about NXP SJA1105 driver

[Vladimir Oltean]

On 4/3/19 12:24 AM, Andrew Lunn wrote:
> > +The switches do not support switch tagging in hardware. But they do support
> > +customizing the TPID by which VLAN traffic is identified as such. The switch
> > +driver is leveraging CONFIG_NET_DSA_TAG_8021Q by requesting that special VLANs
> > +(with a custom TPID of ETH_P_EDSA instead of ETH_P_8021Q)
>
> Hi Vladimir
>
> Reusing ETH_P_EDSA is possibility going to case problems in tcpdump.
> It has code which looks for this Ethertype and uses it to call the
> Marvell EDSA header decoder code. This is not going to work for your
> switch, where you have a normal VLAN header.
>
> I wounder if we should allocate a new EtherType for this application
> of VLANs?
>
>     Andrew

Hi Andrew,

This makes me wonder whether I would be able to use an EtherType range 
to support cascading switch tags on SJA1105.
In theory if I were to consistently lie to all switches within a switch 
tree, I could make all of them see each other's fake VLAN-tagged traffic 
as untagged.
By the way what is the simple ETH_P_DSA used for?

Thank you,
-Vladimir