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Date:   Sun, 4 Jun 2023 15:47:01 +0300
From:   Vladimir Oltean <olteanv@gmail.com>
To:     =?utf-8?B?QXLEsW7DpyDDnE5BTA==?= <arinc.unal@arinc9.com>
Cc:     Sean Wang <sean.wang@mediatek.com>,
        Landen Chao <Landen.Chao@mediatek.com>,
        DENG Qingfang <dqfext@gmail.com>,
        Daniel Golle <daniel@makrotopia.org>,
        Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
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        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Russell King <linux@armlinux.org.uk>,
        Richard van Schagen <richard@routerhints.com>,
        Richard van Schagen <vschagen@cs.com>,
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        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
Subject: Re: [PATCH net-next 27/30] net: dsa: mt7530: introduce BPDU trapping
 for MT7530 switch
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On Sun, Jun 04, 2023 at 12:39:33PM +0300, Arınç ÜNAL wrote:
> On 4.06.2023 12:23, Vladimir Oltean wrote:
> > On Sun, Jun 04, 2023 at 11:51:33AM +0300, Arınç ÜNAL wrote:
> > > > If the switch doesn't currently trap BPDUs, isn't STP broken?
> > > 
> > > No, the BPDU_PORT_FW bits are 0 after reset. The MT7620 programming guide
> > > states that frames with 01:80:C2:00:00:00 MAC DA (which is how the BPDU
> > > distinction is being made) will follow the system default which means the
> > > BPDUs will be treated as normal multicast frames.
> > > 
> > > Only if all 3 bits are set will the BPDUs be dropped.
> > 
> > Right, if you don't trap BPDUs just to the CPU but flood them, I believe
> > the STP protocol won't behave properly with switching loops. Worth testing.
> 
> I've got no interest spending time playing around with STP at the moment so
> I'm going to pass.

You can at the very least move it towards the beginning of the net-next patch
set, so that we can be sure it doesn't depend on the other refactoring work,
in case someone in the future makes a request for the patch to be backported
to stable.