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

[Vladimir Oltean]

On Fri, Jul 30, 2021 at 11:45:41PM +0800, DENG Qingfang wrote:
> 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.

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.

> 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.