linux-kernel - Re: [PATCH net-next v3 6/6] net: lan966x: Add switchdev support

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Date:   Mon, 13 Dec 2021 14:29:08 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>
Subject: Re: [PATCH net-next v3 6/6] net: lan966x: Add switchdev support

On Mon, Dec 13, 2021 at 03:26:56PM +0100, Horatiu Vultur wrote:
> > They are independent of each other. You deduce the interface on which
> > the notifier was emitted using switchdev_notifier_info_to_dev() and act
> > upon it, if lan966x_netdevice_check() is true. The notifier handling
> > code itself is stateless, all the state is per port / per switch.
> > If you register one notifier handler per switch, lan966x_netdevice_check()
> > would return true for each notifier handler instance, and you would
> > handle each event twice, would you not?
> 
> That is correct, I will get the event twice which is a problem in the
> lan966x. The function lan966x_netdevice_check should be per instance, in
> this way each instance can filter the events.
> The reason why I am putting the notifier_block inside lan966x is to be
> able to get to the instance of lan966x even if I get a event that is not
> for lan966x port.

That isn't a problem, every netdevice notifier still sees all events.
DSA intercepts a lot of events which aren't directly emitted for its own
interfaces. You don't gain much by having one more, if anything.

> > notifier handlers should be registered as singletons, like other drivers
> > do.
> 
> It looks like not all the other driver register them as singletone. For
> example: prestera, mlx5, sparx5. (I just have done a git grep for
> register_switchdev_notifier, I have not looked in details at the
> implementation).

Not all driver writers may have realized that it is an issue that needs
to be thought of.