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

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Date:   Mon, 13 Dec 2021 15:26:56 +0100
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Vladimir Oltean <vladimir.oltean@....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

The 12/13/2021 13:43, Vladimir Oltean wrote:
> 
> On Mon, Dec 13, 2021 at 11:25:29AM +0100, Horatiu Vultur wrote:
> > The 12/09/2021 17:43, Horatiu Vultur wrote:
> > > > > +int lan966x_register_notifier_blocks(struct lan966x *lan966x)
> > > > > +{
> > > > > +     int err;
> > > > > +
> > > > > +     lan966x->netdevice_nb.notifier_call = lan966x_netdevice_event;
> > > > > +     err = register_netdevice_notifier(&lan966x->netdevice_nb);
> > > > > +     if (err)
> > > > > +             return err;
> > > > > +
> > > > > +     lan966x->switchdev_nb.notifier_call = lan966x_switchdev_event;
> > > > > +     err = register_switchdev_notifier(&lan966x->switchdev_nb);
> > > > > +     if (err)
> > > > > +             goto err_switchdev_nb;
> > > > > +
> > > > > +     lan966x->switchdev_blocking_nb.notifier_call = lan966x_switchdev_blocking_event;
> > > > > +     err = register_switchdev_blocking_notifier(&lan966x->switchdev_blocking_nb);
> > > > > +     if (err)
> > > > > +             goto err_switchdev_blocking_nb;
> > > > > +
> > > > > +     lan966x_owq = alloc_ordered_workqueue("lan966x_order", 0);
> > > > > +     if (!lan966x_owq) {
> > > > > +             err = -ENOMEM;
> > > > > +             goto err_switchdev_blocking_nb;
> > > > > +     }
> > > >
> > > > These should be singleton objects, otherwise things get problematic if
> > > > you have more than one switch device instantiated in the system.
> > >
> > > Yes, I will update this.
> >
> > Actually I think they need to be part of lan966x.
> > Because we want each lan966x instance to be independent of each other.
> > This is not seen in this version but is more clear in the next version
> > (v4).
> 
> 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.

> 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).


-- 
/Horatiu