[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 at gmail.com wrote:
>> From: Arınç ÜNAL <arinc.unal at arinc9.com>
>>
>> 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 at arinc9.com>
>> Signed-off-by: Arınç ÜNAL <arinc.unal at arinc9.com>
>> ---
>>   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.

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