netdev - Re: [PATCH net-next 0/3] bridge: dsa: switchdev: mv88e6xxx: Implement local

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Date:   Thu, 17 Mar 2022 16:05:25 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Mattias Forsblad <mattias.forsblad@...il.com>,
        netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Mattias Forsblad <mattias.forsblad+netdev@...il.com>,
        Joachim Wiberg <troglobit@...il.com>,
        Ido Schimmel <idosch@...sch.org>,
        "Allan W. Nielsen" <allan.nielsen@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>
Subject: Re: [PATCH net-next 0/3] bridge: dsa: switchdev: mv88e6xxx:
 Implement local_receive bridge flag

Hello Tobias,

On Tue, Mar 01, 2022 at 10:04:09PM +0100, Tobias Waldekranz wrote:
> On Tue, Mar 01, 2022 at 09:14, Florian Fainelli <f.fainelli@...il.com> wrote:
> > On 3/1/2022 4:31 AM, Mattias Forsblad wrote:
> >> Greetings,
> >> 
> >> This series implements a new bridge flag 'local_receive' and HW
> >> offloading for Marvell mv88e6xxx.
> >> 
> >> When using a non-VLAN filtering bridge we want to be able to limit
> >> traffic to the CPU port to lessen the CPU load. This is specially
> >> important when we have disabled learning on user ports.
> >> 
> >> A sample configuration could be something like this:
> >> 
> >>         br0
> >>        /   \
> >>     swp0   swp1
> >> 
> >> ip link add dev br0 type bridge stp_state 0 vlan_filtering 0
> >> ip link set swp0 master br0
> >> ip link set swp1 master br0
> >> ip link set swp0 type bridge_slave learning off
> >> ip link set swp1 type bridge_slave learning off
> >> ip link set swp0 up
> >> ip link set swp1 up
> >> ip link set br0 type bridge local_receive 0
> >> ip link set br0 up
> >> 
> >> The first part of the series implements the flag for the SW bridge
> >> and the second part the DSA infrastructure. The last part implements
> >> offloading of this flag to HW for mv88e6xxx, which uses the
> >> port vlan table to restrict the ingress from user ports
> >> to the CPU port when this flag is cleared.
> >
> > Why not use a bridge with VLAN filtering enabled? I cannot quite find it 
> > right now, but Vladimir recently picked up what I had attempted before 
> > which was to allow removing the CPU port (via the bridge master device) 
> > from a specific group of VLANs to achieve that isolation.
> >
> 
> Hi Florian,
> 
> Yes we are aware of this work, which is awesome by the way! For anyone
> else who is interested, I believe you are referring to this series:
> 
> https://lore.kernel.org/netdev/20220215170218.2032432-1-vladimir.oltean@nxp.com/
> 
> There are cases though, where you want a TPMR-like setup (or "dumb hub"
> mode, if you will) and ignore all tag information.
> 
> One application could be to use a pair of ports on a switch as an
> ethernet extender/repeater for topologies that span large physical
> distances. If this repeater is part of a redundant topology, you'd to
> well to disable learning, in order to avoid dropping packets when the
> surrounding active topology changes. This, in turn, will mean that all
> flows will be classified as unknown unicast. For that reason it is very
> important that the CPU be shielded.

So have you seriously considered making the bridge ports that operate in
'dumb hub' mode have a pvid which isn't installed as a 'self' entry on
the bridge device?

> You might be tempted to solve this using flooding filters of the
> switch's CPU port, but these go out the window if you have another
> bridge configured, that requires that flooding of unknown traffic is
> enabled.

Not if CPU flooding can be managed on a per-user-port basis.

> Another application is to create a similar setup, but with three ports,
> and have the third one be used as a TAP.

Could you expand more on this use case?

> >> Reviewed-by: Tobias Waldekranz <tobias@...dekranz.com>
> >
> > I don't believe this tag has much value since it was presumably carried 
> > over from an internal review. Might be worth adding it publicly now, though.
> 
> I think Mattias meant to replicate this tag on each individual
> patch. Aside from that though, are you saying that a tag is never valid
> unless there is a public message on the list from the signee? Makes
> sense I suppose. Anyway, I will send separate tags for this series.