net: dsa: sja1105: add bridge TX data plane offload based on tag_8021q
The main desire for having this feature in sja1105 is to support network stack termination for traffic coming from a VLAN-aware bridge. For sja1105, offloading the bridge data plane means sending packets as-is, with the proper VLAN tag, to the chip. The chip will look up its FDB and forward them to the correct destination port. But we support bridge data plane offload even for VLAN-unaware bridges, and the implementation there is different. In fact, VLAN-unaware bridging is governed by tag_8021q, so it makes sense to have the .bridge_fwd_offload_add() implementation fully within tag_8021q. The key difference is that we only support 1 VLAN-aware bridge, but we support multiple VLAN-unaware bridges. So we need to make sure that the forwarding domain is not crossed by packets injected from the stack. For this, we introduce the concept of a tag_8021q TX VLAN for bridge forwarding offload. As opposed to the regular TX VLANs which contain only 2 ports (the user port and the CPU port), a bridge data plane TX VLAN is "multicast" (or "imprecise"): it contains all the ports that are part of a certain bridge, and the hardware will select where the packet goes within this "imprecise" forwarding domain. Each VLAN-unaware bridge has its own "imprecise" TX VLAN, so we make use of the unique "bridge_num" provided by DSA for the data plane offload. We use the same 3 bits from the tag_8021q VLAN ID format to encode this bridge number. Note that these 3 bit positions have been used before for sub-VLANs in best-effort VLAN filtering mode. The difference is that for best-effort, the sub-VLANs were only valid on RX (and it was documented that the sub-VLAN field needed to be transmitted as zero). Whereas for the bridge data plane offload, these 3 bits are only valid on TX. Signed-off-by:Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
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