netdev - Re: commit 4c7ea3c0791e (net: dsa: mv88e6xxx: disable SA learning for DSA and CPU ports)

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Date:   Mon, 18 Jan 2021 20:10:55 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Network Development <netdev@...r.kernel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Vladimir Oltean <olteanv@...il.com>
Subject: Re: commit 4c7ea3c0791e (net: dsa: mv88e6xxx: disable SA learning for DSA and CPU ports)

On Mon, Jan 18, 2021 at 20:01, Andrew Lunn <andrew@...n.ch> wrote:
> On Mon, Jan 18, 2021 at 07:30:49PM +0100, Tobias Waldekranz wrote:
>> On Mon, Jan 18, 2021 at 18:50, Andrew Lunn <andrew@...n.ch> wrote:
>> >> I suppose the real solution is having userspace do some "bridge mdb add"
>> >> yoga, but since no code currently uses
>> >> MV88E6XXX_G1_ATU_DATA_STATE_MC_STATIC_DA_MGMT, I don't think there's any
>> >> way to actually achieve this. And I have no idea how to represent the
>> >> requirement that "frames with this multicast DA are only to be directed
>> >> at the CPU" in a hardware-agnostic way.
>> >
>> > The switchdev interface for this exists, because there can be
>> > multicast listeners on the bridge. When they join a group, they ask
>> > the switch to put in a HOST MDB, which should cause the traffic for
>> 
>> That is not quite the same thing as "management" though. Adding the
>> group to the host MDB will not allow it to pass through blocked (in the
>> STP sense) ports for example. With a management entry, the switch will
>> trap the packet with a TO_CPU tag, which means no ingress policy can get
>> in the way of it reaching the CPU.
>
> Ah, yes. I don't suppose the DA is part of the special group which the
> switch will recognise as management and pass it on?
>
> 01:80:c2:00:00:00 - 01:80:c2:00:00:07
> 01:80:c2:00:00:08 - 01:80:c2:00:00:0f
> 01:80:c2:00:00:20 - 01:80:c2:00:00:27
> 01:80:c2:00:00:28 - 01:80:c2:00:00:2f

Unfortunately there are many protocols that live outside of the IEEE
range. ERP(S) which Rasmus was talking about uses a range assigned to
ITU IIRC. MRP a third one I believe.

The Reserved2CPU functionality has an additional deficiency vs. separate
management entries: they all use the same priority. This means that you
must assign LLDP frames to the same queue as STP for example, which is
typically not what you want. With a management entry (with priority
override) you can set them individually.