netdev - Re: [RFC net-next 1/2] net: dsa: tag_mtk: skip address learning on transmit to standalone ports

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Message-ID: <20210730173902.vezop3n55bk63o6f@skbuf>
Date:   Fri, 30 Jul 2021 20:39:02 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next 1/2] net: dsa: tag_mtk: skip address learning on
 transmit to standalone ports

On Sat, Jul 31, 2021 at 01:32:03AM +0800, DENG Qingfang wrote:
> On Fri, Jul 30, 2021 at 07:24:03PM +0300, Vladimir Oltean wrote:
> > Considering that you also have the option of setting
> > ds->assisted_learning_on_cpu_port = true and this will have less false
> > positives, what are the reasons why you did not choose that approach?
> 
> You're right. Hardware learning on CPU port does have some limitations.
> 
> I have been testing a multi CPU ports patch, and assisted learning has
> to be used, because FDB entries should be installed like multicast
> ones, which point to all CPU ports.

Ah, mt7530 is one of the switches which has multiple CPU ports, I had
forgotten that. In that case, then static FDB entries are pretty much
the only way to go indeed.

I am going to send a patch series soon to convert sja1105 to assisted
learning too. It doesn't support multiple CPU ports, and it does have
hardware learning on the CPU port, but it can be arranged in cross-chip
topologies where each switch has its own CPU port, so from DSA's
perspective, it is as though we are dealing with a multi-CPU port switch
(the DSA tree does have multiple CPUs, in fact).  I have been
obsessively testing this configuration for the past few weeks and I
think the assisted learning functionality works fairly well by now.