Re: [PATCH net] net: dsa: b53: be VLAN unaware when not filtering

[Semih Baskan]

Hi Jonas,

On Thu, Aug 13, 2026 at 10:08 AM Jonas Gorski <jonas.gorski@xxxxxxxxx> wrote:
> Right, that would be the quick workaround to allow functionality. We
> just need to not mark them as forwarded, as DROP_VTABLE_MISS=0 will
> have them sent to CPU already.

On bcm5301x, miss frames reach the CPU only with port 8 as the sole
management port.

All measured on the BCM53011, DROP_VTABLE_MISS=0 throughout:

- In-tree topology (port 5 as CPU): a tagged frame with a VID absent
  from the VLAN table reaches no CPU port, 0 of 7. Already reported
  in the offload series thread.
- All three CPU ports enabled per the in-tree bcm-ns.dtsi, with
  Rafal's V3 patches 1 and 2 applied so DSA prefers port 8, measured
  yesterday: still 0 of 7. GMNGCFG reads 0xc2, dual IMP mode, and in
  that mode the miss path delivers to no port at all; bringing the
  port 5 conduit up or down changes nothing.
- Port 8 as the ONLY enabled CPU port (FRM_MNGP=0b10): miss frames
  are delivered to the CPU, indiscriminately.

So a software bridging fallback that relies on miss-to-CPU delivery
works on chips like BCM63268/BCM53115, where you measured the CPU
copy, but on bcm5301x it additionally requires either a single IMP DT
(disabling ports 5 and 7, as the Netgear R8000 and Linksys Panamera
do today) or driver code that forces FRM_MNGP to 0b10 when port 8
is the conduit. Rafal's pending "ARM: dts: BCM5301X: Enable extra
CPU ports for Netgear R8000" re-enables those two ports on the
R8000. On the port 5 DTs it would receive nothing.

Best regards,
Semih