netdev - Re: [PATCH net-next 2/6] net: dsa: vsc73xx: add port_stp_state

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Message-ID: <70f3b45f-7c57-4394-b96e-20a014718f5f@lunn.ch>
Date: Thu, 22 Jun 2023 15:01:02 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Paweł Dembicki <paweldembicki@...il.com>
Cc: netdev@...r.kernel.org, linus.walleij@...aro.org,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/6] net: dsa: vsc73xx: add port_stp_state_set
 function

On Wed, Jun 21, 2023 at 10:38:22PM +0200, Paweł Dembicki wrote:
> śr., 21 cze 2023 o 21:33 Andrew Lunn <andrew@...n.ch> napisał(a):
> >
> > > +     struct vsc73xx *vsc = ds->priv;
> > > +     /* FIXME: STP frames isn't forwarded at this moment. BPDU frames are
> > > +      * forwarded only from to PI/SI interface. For more info see chapter
> > > +      * 2.7.1 (CPU Forwarding) in datasheet.
> >
> > Do you mean the CPU never gets to see the BPDU frames?
> >
> > Does the hardware have any sort of packet matching to trap frames to
> > the CPU? Can you match on the destination MAC address
> > 01:80:C2:00:00:00 ?
> >
> 
> Analyzer in VSC73XX switches can send some kind of packages to (and
> from) processor via registers available from SPI/Platform BUS (for
> some external analysis).  In some cases it's possible to configure: if
> packet will be copied or forwarded to this special CPU queue.  But
> BPDU frames could be sent to processor via CPU queue only. So It's
> impossible to forward bridge control data via rgmii interface.

So am i correct in saying, if you actually enable STP, and it decides
to block a port, the BPDUs are also blocked. After a while it will
decide the peer has gone, and unblock the port. A broadcast storm will
then happen for a while, until a BPDU is received, at which point it
will block the port again.

     Andrew