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Date:   Mon, 17 Apr 2023 14:53:30 +0200
From:   Simon Horman <simon.horman@corigine.com>
To:     Vladimir Oltean <vladimir.oltean@nxp.com>
Cc:     netdev@vger.kernel.org, Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Claudiu Manoil <claudiu.manoil@nxp.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        UNGLinuxDriver@microchip.com,
        Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/7] net: mscc: ocelot: remove struct
 ocelot_mm_state :: lock
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References: <20230415170551.3939607-1-vladimir.oltean@nxp.com>
 <20230415170551.3939607-3-vladimir.oltean@nxp.com>
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On Sat, Apr 15, 2023 at 08:05:46PM +0300, Vladimir Oltean wrote:
> Unfortunately, the workarounds for the hardware bugs make it pointless
> to keep fine-grained locking for the MAC Merge state of each port.
> 
> Our vsc9959_cut_through_fwd() implementation requires
> ocelot->fwd_domain_lock to be held, in order to serialize with changes
> to the bridging domains and to port speed changes (which affect which
> ports can be cut-through). Simultaneously, the traffic classes which can
> be cut-through cannot be preemptible at the same time, and this will
> depend on the MAC Merge layer state (which changes from threaded
> interrupt context).
> 
> Since vsc9959_cut_through_fwd() would have to hold the mm->lock of all
> ports for a correct and race-free implementation with respect to
> ocelot_mm_irq(), in practice it means that any time a port's mm->lock is
> held, it would potentially block holders of ocelot->fwd_domain_lock.
> 
> In the interest of simple locking rules, make all MAC Merge layer state
> changes (and preemptible traffic class changes) be serialized by the
> ocelot->fwd_domain_lock.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Simon Horman <simon.horman@corigine.com>