Re: [PATCH net-next v2 0/4] add HSR offloading support for DSA switches

On Tue, Feb 09, 2021 at 11:04:08AM -0600, George McCollister wrote:

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In the DSA layer (dsa_slave_changeupper), could we merge the two HSR
join/leave calls somehow? My guess is all drivers are going to end up
having to do the same dance of deferring configuration until both ports
are known.

Describe what you mean a bit more. Do you mean join and leave should
each only be called once with both hsr ports being passed in?

Exactly. Maybe we could use `netdev_for_each_lower_dev` to figure out if
the other port has already been switched over to the new upper or
something. I find it hard to believe that there is any hardware out
there that can do something useful with a single HSR/PRP port anyway.

If one port failed maybe it would still be useful to join one port if
the switch supported it? Maybe this couldn't ever happen anyway due
the way hsr is designed.

How were you thinking this would work? Would it just not use
dsa_port_notify() and call a switch op directly after the second
port's dsa_slave_changeupper() call? Or would we instead keep port
notifiers and calls to dsa_switch_hsr_join for each port and just make
dsa_switch_hsr_join() not call the switch op to create the HSR until
the second port called it? I'm not all that familiar with how these
dsa notifiers work and would prefer to stick with using a similar
mechanism to the bridge and lag support. It would be nice to get some
feedback from the DSA maintainers on how they would prefer it to work
if they indeed had a preference at all.

Even though I understand where this is coming from, I have grown to
dislike overengineered solutions. DSA is there to standardize how an
Ethernet-connected switch interacts with the network stack, not to be
the middle man that tries to offer a lending hand everywhere.
If there is a 50/50 chance that this extra logic in the DSA mid layer
will not be needed for the second switch that offloads HSR/PRP, then I'd
go with "don't do it". Just emit a hsr_join for both ports and let the
driver deal with it.