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

[Arınç ÜNAL]

On 26.05.2023 20:02, Vladimir Oltean wrote:
> On Mon, May 22, 2023 at 03:15:29PM +0300, arinc9.unal@xxxxxxxxx wrote:
> > From: Arınç ÜNAL <arinc.unal@xxxxxxxxxx>
> >
> > The MT753X switches are capable of trapping certain frames. Introduce
> > trapping BPDUs to the CPU port for the MT7530 switch.
> >
> > BPDUs will be trapped to the numerically smallest CPU port which is affine
> > to the DSA conduit interface that is set up. The BPDUs won't necessarily be
> > trapped to the CPU port the user port, which these BPDUs are received from,
> > is affine to.
> >
> > Tested-by: Arınç ÜNAL <arinc.unal@xxxxxxxxxx>
> > Signed-off-by: Arınç ÜNAL <arinc.unal@xxxxxxxxxx>
> > ---
> >   drivers/net/dsa/mt7530.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> > index cd16911fcb01..2fb4b0bc6335 100644
> > --- a/drivers/net/dsa/mt7530.c
> > +++ b/drivers/net/dsa/mt7530.c
> > @@ -2223,6 +2223,10 @@ mt7530_setup(struct dsa_switch *ds)
> >   	val |= MHWTRAP_MANUAL;
> >   	mt7530_write(priv, MT7530_MHWTRAP, val);
> >   
> > +	/* Trap BPDUs to the CPU port */
> > +	mt7530_rmw(priv, MT753X_BPC, MT753X_BPDU_PORT_FW_MASK,
> > +		   MT753X_BPDU_CPU_ONLY);
> > +
>
> 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.

> ip link add br0 type bridge stp_state 1
> (with or without a userspace helper installed at /sbin/bridge-stp
> for more modern protocols than the original 802.1D STP)

For reference, the mstpd package on Buildroot includes this.

Arınç