netdev - Re: [PATCH net-next v2 0/7] net: lan966x: Add lag support

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Date:   Fri, 1 Jul 2022 16:34:15 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2 0/7] net: lan966x: Add lag support

On Thu, Jun 30, 2022 at 09:08:46PM +0200, Horatiu Vultur wrote:
> > I've downloaded and applied your patches and I have some general feedback.
> > Some of it relates to changes which were not made and hence I couldn't
> > have commented on the patches themselves, so I'm posting it here.
> > 
> > 1. switchdev_bridge_port_offload() returns an error code if object
> > replay failed, or if it couldn't get the port parent id, or if the user
> > tries to join a lan966x port and a port belonging to another switchdev
> > driver to the same LAG. It would be good to propagate this error and not
> > ignore it.
> 
> Yes, I will do that.
> 
> What about the case when the other port is not a switchdev port. For
> example:
> ip link set dev eth0 master bond0
> ip link set dev dummy master bond0
> ip link set dev bond0 master br0
> 
> At the last line, I was expecting to get an error.

switchdev_bridge_port_offload() currently only detects mismatched port
parent IDs, so it will not detect this condition where one bond slave is
switchdev and the other isn't. This is because the non-switchdev bond
slave does not even call switchdev_bridge_port_offload(), it's completely
silent from the perspective of the bridge.
Fact is that we don't have a common layer that enforces all common sense
netdev adjacency restrictions with switchdev, and that is one of the big
problems of the system.

> > 6. You are missing LAG FDB migration logic in lan966x_lag_port_join().
> > Specifically, you assume that the lan966x_lag_first_port() will never
> > change, probably because you just make the switch ports join the LAG in
> > the order 1, 2, 3. But they can also join in the order 3, 2, 1.
> 
> It would work, but there will be problems when the ports start to leave
> the LAG.
> It would work because all the ports under the LAG will have the same
> value in PGID_ID for DST_IDX. So if the MAC entry points to any of
> this entries will be OK.

OK, I forgot DEST_IDX selects PGID and not logical port ID directly.

> The problem is when the port leaves the LAG, if the MAC entry points
> to the port that left the LAG then is not working anymore.
> I will fix this in the next series.