netdev - Re: [RFC PATCH v2 net-next 04/16] net: dsa: sync up with bridge port's STP state when joining

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Date:   Mon, 22 Mar 2021 11:29:54 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ido Schimmel <idosch@...sch.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com, Vadym Kochan <vkochan@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Ivan Vecera <ivecera@...hat.com>, linux-omap@...r.kernel.org,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [RFC PATCH v2 net-next 04/16] net: dsa: sync up with bridge port's STP state when joining

On Fri, Mar 19, 2021 at 01:18, Vladimir Oltean <olteanv@...il.com> wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
>
> It may happen that we have the following topology:
>
> ip link add br0 type bridge stp_state 1
> ip link add bond0 type bond
> ip link set bond0 master br0
> ip link set swp0 master bond0
> ip link set swp1 master bond0
>
> STP decides that it should put bond0 into the BLOCKING state, and
> that's that. The ports that are actively listening for the switchdev
> port attributes emitted for the bond0 bridge port (because they are
> offloading it) and have the honor of seeing that switchdev port
> attribute can react to it, so we can program swp0 and swp1 into the
> BLOCKING state.
>
> But if then we do:
>
> ip link set swp2 master bond0
>
> then as far as the bridge is concerned, nothing has changed: it still
> has one bridge port. But this new bridge port will not see any STP state
> change notification and will remain FORWARDING, which is how the
> standalone code leaves it in.
>
> Add a function to the bridge which retrieves the current STP state, such
> that drivers can synchronize to it when they may have missed switchdev
> events.
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---

Reviewed-by: Tobias Waldekranz <tobias@...dekranz.com>