Subject: Re: [PATCH v2 net-next 2/4] net: dsa: Link aggregation support

From: Tobias Waldekranz <[email-masked]>
Date: Tue, 01 Dec 2020 15:29:53 +0100

On Tue, Dec 01, 2020 at 16:03, Vladimir Oltean <[email-masked]> wrote:
> On Mon, Nov 30, 2020 at 03:06:08PM +0100, Tobias Waldekranz wrote:
>> When a LAG joins a bridge, the DSA subsystem will treat that as each
>> individual port joining the bridge. The driver may look at the port's
>> LAG pointer to see if it is associated with any LAG, if that is
>> required. This is analogue to how switchdev events are replicated out
>> to all lower devices when reaching e.g. a LAG.
>
> Agree with the principle. But doesn't that mean that this code:
>
> static int dsa_slave_switchdev_blocking_event(struct notifier_block *unused,
> 					      unsigned long event, void *ptr)
> {
> 	struct net_device *dev = switchdev_notifier_info_to_dev(ptr);
> 	int err;
>
> 	switch (event) {
> 	case SWITCHDEV_PORT_OBJ_ADD:
> 		err = switchdev_handle_port_obj_add(dev, ptr,
> 						    dsa_slave_dev_check,
> 						    dsa_slave_port_obj_add);
> 		return notifier_from_errno(err);
> 	case SWITCHDEV_PORT_OBJ_DEL:
> 		err = switchdev_handle_port_obj_del(dev, ptr,
> 						    dsa_slave_dev_check,
> 						    dsa_slave_port_obj_del);
> 		return notifier_from_errno(err);
> 	case SWITCHDEV_PORT_ATTR_SET:
> 		err = switchdev_handle_port_attr_set(dev, ptr,
> 						     dsa_slave_dev_check,
> 						     dsa_slave_port_attr_set);
> 		return notifier_from_errno(err);
> 	}
>
> 	return NOTIFY_DONE;
> }
>
> should be replaced with something that also reacts to the case where
> "dev" is a LAG? Like, for example, I imagine that a VLAN installed on a
> bridge port that is a LAG should be propagated to the switch ports
> beneath that LAG. Similarly for all bridge attributes.

That is exactly what switchdev_handle_* does, no? It is this exact
behavior that my statement about switchdev event replication references.

> As for FDB and MDB addresses, I think they should be propagated towards
> a "logical port" corresponding to the LAG upper. I don't know how the
> mv88e6xxx handles this.

mv88e6xxx differentiates between multicast and unicast entries. So MDB
entries fit very well with the obj_add/del+replication. Unicast entries
will have use "lagX" as its destination, so in that case we need a new
dsa op along the lines of "lag_fdb_add/del".