netdev - Re: [PATCH v3 net-next 06/24] net: dsa: Call driver's setup callback after setting up its switchdev notifier

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Message-ID: <20190413150533.GA17901@lunn.ch>
Date:   Sat, 13 Apr 2019 17:05:33 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     f.fainelli@...il.com, vivien.didelot@...il.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, georg.waibel@...sor-technik.de
Subject: Re: [PATCH v3 net-next 06/24] net: dsa: Call driver's setup callback
 after setting up its switchdev notifier

On Sat, Apr 13, 2019 at 04:28:04AM +0300, Vladimir Oltean wrote:
> This allows the driver to perform some manipulations of its own during
> setup, using generic switchdev calls. Having the notifiers registered at
> setup time is important because otherwise any switchdev transaction
> emitted during this time would be ignored (dispatched to an empty call
> chain).
> 
> One current usage scenario is for the driver to request DSA to set up
> 802.1Q based switch tagging for its ports.
> 
> There is no danger for the driver setup code to start racing now with
> switchdev events emitted from the network stack (such as bridge core)
> even if the notifier is registered earlier. This is because the network
> stack needs a net_device as a vehicle to perform switchdev operations,
> and the slave net_devices are registered later than the core driver
> setup anyway (ds->ops->setup in dsa_switch_setup vs dsa_port_setup).
> 
> Luckily DSA doesn't need a net_device to carry out switchdev callbacks,
> and therefore drivers shouldn't assume either that net_devices are
> available at the time their switchdev callbacks get invoked.

Hi Vladimir

Thanks for adding this explanation to the commit message.

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew