netdev - Re: [PATCH v2 net] net: dsa: microchip: make learning configurable and keep it off while standalone

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Date:   Tue, 23 Aug 2022 14:38:31 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Woojung Huh <woojung.huh@...rochip.com>,
        Arun Ramadoss <arun.ramadoss@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Brian Hutchinson <b.hutchman@...il.com>
Subject: Re: [PATCH v2 net] net: dsa: microchip: make learning configurable
 and keep it off while standalone

On Thu, 18 Aug 2022 19:48:09 +0300 Vladimir Oltean wrote:
> Address learning should initially be turned off by the driver for port
> operation in standalone mode, then the DSA core handles changes to it
> via ds->ops->port_bridge_flags().
> 
> Leaving address learning enabled while ports are standalone breaks any
> kind of communication which involves port B receiving what port A has
> sent. Notably it breaks the ksz9477 driver used with a (non offloaded,
> ports act as if standalone) bonding interface in active-backup mode,
> when the ports are connected together through external switches, for
> redundancy purposes.
> 
> This fixes a major design flaw in the ksz9477 and ksz8795 drivers, which
> unconditionally leave address learning enabled even while ports operate
> as standalone.
> 
> Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
> Link: https://lore.kernel.org/netdev/CAFZh4h-JVWt80CrQWkFji7tZJahMfOToUJQgKS5s0_=9zzpvYQ@mail.gmail.com/
> Reported-by: Brian Hutchinson <b.hutchman@...il.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
> v1->v2: targeting the 6.0 release candidates as opposed to the 5.19 rc's
>         from v1.
> 
> Again, this is compile-tested only, but the equivalent change was
> confirmed by Brian as working on a 5.10 kernel.
> 
> @maintainers: when should I submit the backports to "stable", for older
> trees?

"when" as is how long after Thu PR or "when" as in under what
conditions?