[RFC net-next 2/2] net: dsa: mt7530: trap packets from standalone ports to the CPU

[DENG Qingfang]

On Fri, Jul 30, 2021 at 07:18:52PM +0300, Vladimir Oltean wrote:
> > It turns out that only PVC.VLAN_ATTR contributes to VLAN awareness.
> > Port matrix mode just skips the VLAN table lookup. The reference
> > manual is somehow misleading when describing PORT_VLAN modes (See Page
> > 17 of MT7531 Reference Manual, available at
> > http://wiki.banana-pi.org/Banana_Pi_BPI-R64#Resources). It states that
> > PORT_MEM (VLAN port member) is used for destination if the VLAN table
> > lookup hits, but actually it uses **PORT_MEM & PORT_MATRIX** (bitwise
> > AND of VLAN port member and port matrix) instead, which means we can
> > have two or more separate VLAN-aware bridges with the same PVID and
> > traffic won't leak between them.
> 
> Ah, but it's not completely misleading. It does say:
> 
> 	2'b01: Fallback mode
> 
> 	Enable 802.1Q function for all the received frames.
> 	Do not discard received frames due to ingress membership violation.
> 	**Frames whose VID is missed on the VLAN table will be filtered
> 	by the Port Matrix Member**.
> 
> (emphasis mine on the last paragraph)
> 
> > So I came up with a solution: Set PORT_VLAN to fallback mode when in
> > VLAN-unaware mode, this way, even VLAN-unaware bridges will use
> > independent VLAN filtering.
> 
> If you did indeed test that the Port Matrix is still used to enforce
> separation between ports if the VLAN table _does_ match and we're in
> fallback mode, then we should be okay.

Yes, that's what I mean. Tested as well.

> 
> > Then assign all standalone ports to a reserved VLAN.
> 
> You mean all standalone ports to the same VLAN ID, like 4095, or each
> standalone port to a separate reserved VLAN ID? As long as address
> learning is disabled on the standalone ports, I guess using a single
> VLAN ID like 4095 for all of them is just fine, the Port Matrix will
> take care of the rest.

I just found a cleaner solution: Leaving standalone ports in port matrix
mode. As all bridges use independent VLAN learning, standalone ports'
FDB lookup with FID 0 won't hit.