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    SubjectRe: [PATCH net] net: dsa: mt7530: don't change PVC_EG_TAG when CPU port becomes VLAN-aware
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    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@public-files.de>
    > Tested-by: Frank Wunderlich <frank-w@public-files.de>
    > Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

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

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