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net: dsa: act as passthrough for bridge port flags
There are multiple ways in which a PORT_BRIDGE_FLAGS attribute can be expressed by the bridge through switchdev, and not all of them can be emulated by DSA mid-layer API at the same time. One possible configuration is when the bridge offloads the port flags using a mask that has a single bit set - therefore only one feature should change. However, DSA currently groups together unicast and multicast flooding in the .port_egress_floods method, which limits our options when we try to add support for turning off broadcast flooding: do we extend .port_egress_floods with a third parameter which b53 and mv88e6xxx will ignore? But that means that the DSA layer, which currently implements the PRE_BRIDGE_FLAGS attribute all by itself, will see that .port_egress_floods is implemented, and will report that all 3 types of flooding are supported - not necessarily true. Another configuration is when the user specifies more than one flag at the same time, in the same netlink message. If we were to create one individual function per offloadable bridge port flag, we would limit the expressiveness of the switch driver of refusing certain combinations of flag values. For example, a switch may not have an explicit knob for flooding of unknown multicast, just for flooding in general. In that case, the only correct thing to do is to allow changes to BR_FLOOD and BR_MCAST_FLOOD in tandem, and never allow mismatched values. But having a separate .port_set_unicast_flood and .port_set_multicast_flood would not allow the driver to possibly reject that. Also, DSA doesn't consider it necessary to inform the driver that a SWITCHDEV_ATTR_ID_BRIDGE_MROUTER attribute was offloaded, because it just calls .port_egress_floods for the CPU port. When we'll add support for the plain SWITCHDEV_ATTR_ID_PORT_MROUTER, that will become a real problem because the flood settings will need to be held statefully in the DSA middle layer, otherwise changing the mrouter port attribute will impact the flooding attribute. And that's _assuming_ that the underlying hardware doesn't have anything else to do when a multicast router attaches to a port than flood unknown traffic to it. If it does, there will need to be a dedicated .port_set_mrouter anyway. So we need to let the DSA drivers see the exact form that the bridge passes this switchdev attribute in, otherwise we are standing in the way. Therefore we also need to use this form of language when communicating to the driver that it needs to configure its initial (before bridge join) and final (after bridge leave) port flags. The b53 and mv88e6xxx drivers are converted to the passthrough API and their implementation of .port_egress_floods is split into two: a function that configures unicast flooding and another for multicast. The mv88e6xxx implementation is quite hairy, and it turns out that the implementations of unknown unicast flooding are actually the same for 6185 and for 6352: behind the confusing names actually lie two individual bits: NO_UNKNOWN_MC -> FLOOD_UC = 0x4 = BIT(2) NO_UNKNOWN_UC -> FLOOD_MC = 0x8 = BIT(3) so there was no reason to entangle them in the first place. Whereas the 6185 writes to MV88E6185_PORT_CTL0_FORWARD_UNKNOWN of PORT_CTL0, which has the exact same bit index. I have left the implementations separate though, for the only reason that the names are different enough to confuse me, since I am not able to double-check with a user manual. The multicast flooding setting for 6185 is in a different register than for 6352 though. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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