netdev - Re: [PATCH net-next] net: dsa: don't fast age standalone ports

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Date:   Sun, 8 Aug 2021 17:37:04 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH net-next] net: dsa: don't fast age standalone ports

On Sun, Aug 08, 2021 at 02:16:37PM +0300, Vladimir Oltean wrote:
> DSA drives the procedure to flush dynamic FDB entries from a port based
> on the change of STP state: whenever we go from a state where address
> learning is enabled (LEARNING, FORWARDING) to a state where it isn't
> (LISTENING, BLOCKING, DISABLED), we need to flush the existing dynamic
> entries.
> 
> However, there are cases when this is not needed. Internally, when a
> DSA switch interface is not under a bridge, DSA still keeps it in the
> "FORWARDING" STP state. And when that interface joins a bridge, the
> bridge will meticulously iterate that port through all STP states,
> starting with BLOCKING and ending with FORWARDING. Because there is a
> state transition from the standalone version of FORWARDING into the
> temporary BLOCKING bridge port state, DSA calls the fast age procedure.
> 
> Since commit 5e38c15856e9 ("net: dsa: configure better brport flags when
> ports leave the bridge"), DSA asks standalone ports to disable address
> learning. Therefore, there can be no dynamic FDB entries on a standalone
> port. Therefore, it does not make sense to flush dynamic FDB entries on
> one.

Hi Vladimir

Do all DSA drivers actually support disabling learning on a port?  If
there are any which cannot disable learning, we still need the flush
somehow.

	Andrew