[PATCH net] net: dsa: mt7530: don't change PVC_EG_TAG when CPU port becomes VLAN-aware

[Florian Fainelli]

On 2/5/23 06:07, Vladimir Oltean wrote:
> Frank reports that in a mt7530 setup where some ports are standalone and
> some are in a VLAN-aware bridge, 8021q uppers of the standalone ports
> lose their VLAN tag on xmit, as seen by the link partner.
> 
> This seems to occur because once the other ports join the VLAN-aware
> bridge, mt7530_port_vlan_filtering() also calls
> mt7530_port_set_vlan_aware(ds, cpu_dp->index), and this affects the way
> that the switch processes the traffic of the standalone port.
> 
> Relevant is the PVC_EG_TAG bit. The MT7530 documentation says about it:
> 
> EG_TAG: Incoming Port Egress Tag VLAN Attribution
> 0: disabled (system default)
> 1: consistent (keep the original ingress tag attribute)
> 
> My interpretation is that this setting applies on the ingress port, and
> "disabled" is basically the normal behavior, where the egress tag format
> of the packet (tagged or untagged) is decided by the VLAN table
> (MT7530_VLAN_EGRESS_UNTAG or MT7530_VLAN_EGRESS_TAG).
> 
> But there is also an option of overriding the system default behavior,
> and for the egress tagging format of packets to be decided not by the
> VLAN table, but simply by copying the ingress tag format (if ingress was
> tagged, egress is tagged; if ingress was untagged, egress is untagged;
> aka "consistent). This is useful in 2 scenarios:
> 
> - VLAN-unaware bridge ports will always encounter a miss in the VLAN
>    table. They should forward a packet as-is, though. So we use
>    "consistent" there. See commit e045124e9399 ("net: dsa: mt7530: fix
>    tagged frames pass-through in VLAN-unaware mode").
> 
> - Traffic injected from the CPU port. The operating system is in god
>    mode; if it wants a packet to exit as VLAN-tagged, it sends it as
>    VLAN-tagged. Otherwise it sends it as VLAN-untagged*.
> 
> *This is true only if we don't consider the bridge TX forwarding offload
> feature, which mt7530 doesn't support.
> 
> So for now, make the CPU port always stay in "consistent" mode to allow
> software VLANs to be forwarded to their egress ports with the VLAN tag
> intact, and not stripped.
> 
> Link: https://lore.kernel.org/netdev/trinity-e6294d28-636c-4c40-bb8b-b523521b00be-1674233135062@3c-app-gmx-bs36/
> Fixes: e045124e9399 ("net: dsa: mt7530: fix tagged frames pass-through in VLAN-unaware mode")
> Reported-by: Frank Wunderlich <frank-w at public-files.de>
> Tested-by: Frank Wunderlich <frank-w at public-files.de>
> Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>

Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
-- 
Florian