netdev - Re: [PATCH RFC net-next 0/3] Multi-CPU DSA support

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Date:   Sat, 24 Aug 2019 17:56:36 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Marek Behún <marek.behun@....cz>,
        netdev <netdev@...r.kernel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Ahern <dsahern@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH RFC net-next 0/3] Multi-CPU DSA support

> Will DSA assume that all CPU ports are equal in terms of tagging
> protocol abilities? There are switches where one of the CPU ports can
> do tagging and the other can't.

Hi Vladimir

Given the current definition of what a CPU port is, we have to assume
the port is using tags. Frames have to be directed out a specific
egress port, otherwise things like BPDU, PTP will break. You cannot
rely on MAC address learning.

> Is the static assignment between slave and CPU ports going to be the
> only use case? What about link aggregation? Flow steering perhaps?
> And like Andrew pointed out, how do you handle the receive case? What
> happens to flooded frames, will the switch send them to both CPU
> interfaces, and get received twice in Linux? How do you prevent that?

I expect bad things will happen if frames are flooded to multiple CPU
ports. For this to work, the whole switch design needs to support
multiple CPU ports. I doubt this will work on any old switch.

Having a host interface connected to a user port of the switch is a
completely different uses case, and not what this patchset is about.

	   Andrew