netdev - Re: [PATCH net] net: dsa: fix unintended change of bridge interface STP state

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Message-ID: <20190220113822.GD26057@t480s.localdomain>
Date:   Wed, 20 Feb 2019 11:38:22 -0500
From:   Vivien Didelot <vivien.didelot@...il.com>
To:     Russell King <rmk+kernel@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: fix unintended change of bridge interface
 STP state

On Wed, 20 Feb 2019 10:32:52 +0000, Russell King <rmk+kernel@...linux.org.uk> wrote:
> When a DSA port is added to a bridge and brought up, the resulting STP
> state programmed into the hardware depends on the order that these
> operations are performed.  However, the Linux bridge code believes that
> the port is in disabled mode.
> 
> If the DSA port is first added to a bridge and then brought up, it will
> be in blocking mode.  If it is brought up and then added to the bridge,
> it will be in disabled mode.
> 
> This difference is caused by DSA always setting the STP mode in
> dsa_port_enable() whether or not this port is part of a bridge.  Since
> bridge always sets the STP state when the port is added, brought up or
> taken down, it is unnecessary for us to manipulate the STP state.
> 
> Apparently, this code was copied from Rocker, and the very next day a
> similar fix for Rocker was merged but was not propagated to DSA.  See
> e47172ab7e41 ("rocker: put port in FORWADING state after leaving bridge")
> 
> Fixes: b73adef67765 ("net: dsa: integrate with SWITCHDEV for HW bridging")
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>

Reviewed-by: Vivien Didelot <vivien.didelot@...il.com>