net: dsa: tag_8021q: replace the SVL bridging with VLAN-unaware IVL bridging
For VLAN-unaware bridging, tag_8021q uses something perhaps a bit too tied with the sja1105 switch: each port uses the same pvid which is also used for standalone operation (a unique one from which the source port and device ID can be retrieved when packets from that port are forwarded to the CPU). Since each port has a unique pvid when performing autonomous forwarding, the switch must be configured for Shared VLAN Learning (SVL) such that the VLAN ID itself is ignored when performing FDB lookups. Without SVL, packets would always be flooded, since FDB lookup in the source port's VLAN would never find any entry. First of all, to make tag_8021q more palatable to switches which might not support Shared VLAN Learning, let's just use a common VLAN for all ports that are under the same bridge. Secondly, using Shared VLAN Learning means that FDB isolation can never be enforced. But if all ports under the same VLAN-unaware bridge share the same VLAN ID, it can. The disadvantage is that the CPU port can no longer perform precise source port identification for these packets. But at least we have a mechanism which has proven to be adequate for that situation: imprecise RX (dsa_find_designated_bridge_port_by_vid), which is what we use for termination on VLAN-aware bridges. The VLAN ID that VLAN-unaware bridges will use with tag_8021q is the same one as we were previously using for imprecise TX (bridge TX forwarding offload). It is already allocated, it is just a matter of using it. Note that because now all ports under the same bridge share the same VLAN, the complexity of performing a tag_8021q bridge join decreases dramatically. We no longer have to install the RX VLAN of a newly joining port into the port membership of the existing bridge ports. The newly joining port just becomes a member of the VLAN corresponding to that bridge, and the other ports are already members of it from when they joined the bridge themselves. So forwarding works properly. This means that we can unhook dsa_tag_8021q_bridge_{join,leave} from the cross-chip notifier level dsa_switch_bridge_{join,leave}. We can put these calls directly into the sja1105 driver. With this new mode of operation, a port controlled by tag_8021q can have two pvids whereas before it could only have one. The pvid for standalone operation is different from the pvid used for VLAN-unaware bridging. This is done, again, so that FDB isolation can be enforced. Let tag_8021q manage this by deleting the standalone pvid when a port joins a bridge, and restoring it when it leaves it. Signed-off-by:Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
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