Re: [RFC PATCH net-next 00/12] DSA changes for multiple CPU ports (part 3)

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Tue, May 24, 2022 at 02:02:19PM +0200, Ansuel Smith wrote:
> Probably offtopic but I wonder if the use of a LAG as master can
> cause some problem with configuration where the switch use a mgmt port
> to send settings. Wonder if with this change we will have to introduce
> an additional value to declare a management port that will be used since
> master can now be set to various values. Or just the driver will have to
> handle this with its priv struct (think this is the correct solution)
> 
> I still have to find time to test this with qca8k.

Not offtopic, this is a good point. dsa_tree_master_admin_state_change()
and dsa_tree_master_oper_state_change() set various flags in cpu_dp =
master->dsa_ptr. It's unclear if the cpu_dp we assign to a LAG should
track the admin/oper state of the LAG itself or of the physical port.
Especially since the lag->dsa_ptr is the same as one of the master->dsa_ptr.
It's clear that the same structure can't track both states. I'm thinking
we should suppress the NETDEV_CHANGE and NETDEV_UP monitoring from slave.c
on LAG DSA masters, and track only the physical ones. In any case,
management traffic does not really benefit from being sent/received over
a LAG, and I'm thinking we should just use the physical port.
Your qca8k_master_change() function explicitly only checks for CPU port
0, which in retrospect was a very wise decision in terms of forward
compatibility with device trees with multiple CPU ports.