[PATCH net v4 5/7] net: dsa: mt7530: fix handling of LLDP frames

[Arınç ÜNAL]

On 15.06.2023 15:45, Bartel Eerdekens wrote:
> On Wed, Jun 14, 2023 at 6:42 PM Russell King (Oracle)
> <linux at armlinux.org.uk> wrote:
>>
>> On Mon, Jun 12, 2023 at 10:59:43AM +0300, arinc9.unal at gmail.com wrote:
>>> From: Arınç ÜNAL <arinc.unal at arinc9.com>
>>>
>>> LLDP frames are link-local frames, therefore they must be trapped to the
>>> CPU port. Currently, the MT753X switches treat LLDP frames as regular
>>> multicast frames, therefore flooding them to user ports. To fix this, set
>>> LLDP frames to be trapped to the CPU port(s).
>>>
>>> The mt753x_bpdu_port_fw enum is universally used for trapping frames,
>>> therefore rename it and the values in it to mt753x_port_fw.
>>>
>>> For MT7530, LLDP frames received from a user port will be trapped to the
>>> numerically smallest CPU port which is affine to the DSA conduit interface
>>> that is up.
>>>
>>> For MT7531 and the switch on the MT7988 SoC, LLDP frames received from a
>>> user port will be trapped to the CPU port that is affine to the user port
>>> from which the frames are received.
>>>
>>> The bit for R0E_MANG_FR is 27. When set, the switch regards the frames with
>>> :0E MAC DA as management (LLDP) frames. This bit is set to 1 after reset on
>>> MT7530 and MT7531 according to the documents MT7620 Programming Guide v1.0
>>> and MT7531 Reference Manual for Development Board v1.0, so there's no need
>>> to deal with this bit. Since there's currently no public document for the
>>> switch on the MT7988 SoC, I assume this is also the case for this switch.
>>>
>>> Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
>>
>>
>> Patch 4 claims to be a fix for this commit, and introduces one of these
>> modifications to MT753X_BPC, which this patch then changes.
> 
> Let me chime in on this one, as mentioned by Arinç, I am one of the
> requesters of having this patch (and patch 4).
> Patch 4 enables the trapping of BPDU's to the CPU, being STP (Spanning
> Tree) frames. Maybe that should be mentioned, to be clear.

Sure, I can quote the first sentence on the wikipedia page "Bridge 
protocol data unit".

> 
>>
>> On the face of it, it seems this patch is actually a fix to patch 4 as
>> well as the original patch, so does that mean that patch 4 only half
>> fixes a problem?
> 
> This patch then also adds trapping for LLDP frames (Link Layer
> Discovery Protocol) which is a completely different protocol.
> But both rely on trapping frames, instead of forwarding them.

Flooding is a better term. "Trapped" frames are still forwarded, the 
difference is they are forwarded only to the CPU port.

Arınç