Re: [PATCH net-next 27/30] net: dsa: mt7530: introduce BPDU trapping for MT7530 switch

Vladimir Oltean
2023-06-04T12:47:32Z

On Sun, Jun 04, 2023 at 12:39:33PM +0300, Arınç ÜNAL wrote:
> On 4.06.2023 12:23, Vladimir Oltean wrote:
> > On Sun, Jun 04, 2023 at 11:51:33AM +0300, Arınç ÜNAL wrote:
> > > > If the switch doesn't currently trap BPDUs, isn't STP broken?
> > >
> > > No, the BPDU_PORT_FW bits are 0 after reset. The MT7620 programming guide
> > > states that frames with 01:80:C2:00:00:00 MAC DA (which is how the BPDU
> > > distinction is being made) will follow the system default which means the
> > > BPDUs will be treated as normal multicast frames.
> > >
> > > Only if all 3 bits are set will the BPDUs be dropped.
> >
> > Right, if you don't trap BPDUs just to the CPU but flood them, I believe
> > the STP protocol won't behave properly with switching loops. Worth testing.
>
> I've got no interest spending time playing around with STP at the moment so
> I'm going to pass.

You can at the very least move it towards the beginning of the net-next patch
set, so that we can be sure it doesn't depend on the other refactoring work,
in case someone in the future makes a request for the patch to be backported
to stable.