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

[DENG Qingfang]

On Fri, Jul 30, 2021 at 12:50 AM Vladimir Oltean <olteanv at gmail.com> wrote:
> I have the MT7621 GSW, and sadly this reference manual isn't the best in
> explaining what is and what is not possible. For example, I am still not
> clear what is meant by "VID1" and "VID0". Is "VID1" the inner (customer)
> VLAN tag, and "VID0" the outer (service) VLAN tag, or "VID1" means the
> actual VLAN ID 1?
>
> And the bits 3:1 of VAWD1 (VLAN table access register) indicate a FID
> field per VLAN. I cannot find the piece that you quoted in this manual.
> But what I expect to happen for a Transparent Port is that the packets
> are always classified to that port's PVID, and the VLAN Table is looked
> up with that PVID. There, it will find the FID, which this driver
> currently always configures as zero. In my manual's description, in the
> "Transparent Port" chapter, it does explicitly say:
>
>         VID0 and VID1 will store PVID as the default VID which is used
>         to look up the VLAN table.
>
> So I get the impression that the phrase "the VLAN table is not applicable"
> is not quite correct, but I might be wrong...

Alright, I think I've made some progress.
In the current code, we only use two combinations to toggle user
ports' VLAN awareness: one is PCR.PORT_VLAN set to port matrix mode
with PVC.VLAN_ATTR set to transparent port, the other is PCR.PORT_VLAN
set to security mode with PVC.VLAN_ATTR set to user port.

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.

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. Then assign all standalone ports to a
reserved VLAN.