netdev - RE: [PATCH] net: dsa: ksz: Fix port membership

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Date:   Sat, 8 Dec 2018 00:08:45 +0000
From:   <Tristram.Ha@...rochip.com>
To:     <andrew@...n.ch>
CC:     <marex@...x.de>, <f.fainelli@...il.com>,
        <vivien.didelot@...oirfairelinux.com>, <Woojung.Huh@...rochip.com>,
        <UNGLinuxDriver@...rochip.com>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>
Subject: RE: [PATCH] net: dsa: ksz: Fix port membership

> > I think if you do this without setting offload_fwd_mark you will
> > receive duplicate frame.
> 
> I don't think it will, at least not in the normal case. The hardware
> should know the egress port, so there is no need to forward a copy to
> the CPU. The only time it should forward to the CPU is when the egress
> port is not known, so it floods. Without offload_fwd_mark set, the SW
> bridge will flood it back out the ports causing duplication. But that
> is not too bad. The Marvell driver did this for a while and nothing
> bad was reported.

For unicast frames it is okay as the CPU port does not see it after the first
one.  For multicast frames there will be duplicates, and it is tolerated?