Re: [PATCH net-next 2/2] net: dsa: lan9303: Add basic offloading of unicast traffic

[Egil Hjelmeland]

Den 22. sep. 2017 22:08, skrev Andrew Lunn:
> > > I'm wondering how this is supposed to work. Please add a good comment
> > > here, since the hardware is forcing you to do something odd.
> > >
> > > Maybe it would be a good idea to save the STP state in chip.  And then
> > > when chip->is_bridged is set true, change the state in the hardware to
> > > the saved value?
> > >
> > > What happens when port 0 is added to the bridge, there is then a
> > > minute pause and then port 1 is added? I would expect that as soon as
> > > port 0 is added, the STP state machine for port 0 will start and move
> > > into listening and then forwarding. Due to hardware limitations it
> > > looks like you cannot do this. So what state is the hardware
> > > effectively in? Blocking? Forwarding?
> > >
> > > Then port 1 is added. You can then can respect the states. port 1 will
> > > do blocking->listening->forwarding, but what about port 0? The calls
> > > won't get repeated? How does it transition to forwarding?
> > >
> > >    Andrew
> >
> > I see your point with the "minute pause" argument. Although a bit
> > contrived use case, it is easy to fix by caching the STP state, as
> > you suggest. So I can do that.
>
> I don't think it is contrived. I've done bridge configuration by hand
> for testing purposes. I've also set the forwarding delay to very small
> values, so there is a clear race condition here.
>
> > How does other DSA HW chips handle port separation? Knowing that
> > could perhaps help me know what to look for.
>
> They have better hardware :-)
>
> Generally each port is totally independent. You can change the STP
> state per port without restrictions.
We can indeed change the STP state per lan9303 port "without
restrictions".

The point is: Once both external ports are in "forwarding", I see no way
to prevent traffic flowing directly between the external ports.


>        Andrew

Egil