Re: [PATCH v2 net-next 4/5] net: dsa: mv88e6xxx: Improve multichip isolation of standalone ports

[Vladimir Oltean]

On Thu, Feb 03, 2022 at 11:16:56AM +0100, Tobias Waldekranz wrote:
> Given that standalone ports are now configured to bypass the ATU and
> forward all frames towards the upstream port, extend the ATU bypass to
> multichip systems.
> 
> Load VID 0 (standalone) into the VTU with the policy bit set. Since
> VID 4095 (bridged) is already loaded, we now know that all VIDs in use
> are always available in all VTUs. Therefore, we can safely enable
> 802.1Q on DSA ports.
> 
> Setting the DSA ports' VTU policy to TRAP means that all incoming
> frames on VID 0 will be classified as MGMT - as a result, the ATU is
> bypassed on all subsequent switches.
> 
> With this isolation in place, we are able to support configurations
> that are simultaneously very quirky and very useful. Quirky because it
> involves looping cables between local switchports like in this
> example:
> 
>    CPU
>     |     .------.
> .---0---. | .----0----.
> |  sw0  | | |   sw1   |
> '-1-2-3-' | '-1-2-3-4-'
>   $ @ '---'   $ @ % %
> 
> We have three physically looped pairs ($, @, and %).
> 
> This is very useful because it allows us to run the kernel's
> kselftests for the bridge on mv88e6xxx hardware.
> 
> Signed-off-by: Tobias Waldekranz <tobias@xxxxxxxxxxxxxx>
> ---

Reviewed-by: Vladimir Oltean <olteanv@xxxxxxxxx>