Re: [PATCH v3 net-next 5/8] net: dsa: felix: support psfp filter on vsc9959

[Vladimir Oltean]

On Tue, Aug 31, 2021 at 08:59:57AM +0000, Xiaoliang Yang wrote:
> > I think in previous versions you were automatically installing a static MAC table
> > entry when one was not present (either it was absent, or the entry was
> > dynamically learned). Why did that change?
> 
> The PSFP gate and police action are set on ingress port, and "
> tc-filter" has no parameter to set the forward port for the filtered
> stream. And I also think that adding a FDB mac entry in tc-filter
> command is not good.

Fair enough, but if that's what you want, we'll need to think a lot
harder about how this needs to be modeled.

Would you not have to protect against a 'bridge fdb del' erasing your
MAC table entry after you've set up the TSN stream on it?

Right now, DSA does not even call the driver's .port_fdb_del method from
atomic context, just from deferred work context. So even if you wanted
to complain and say "cannot remove FDB entry until SFID stops pointing
at it", that would not be possible with today's code structure.

And what would you do if the bridge wants to delete the FDB entry
irrevocably, like when the user wants to delete the bridge in its
entirety? You would still remain with filters in tc which are not backed
by any MAC table entry.

Hmm..
Either the TSN standards for PSFP and FRER are meant to be implemented
within the bridge driver itself, and not as part of tc, or the Microchip
implementation is very weird for wiring them into the bridge MAC table.

Microchip people, any comments?