``BR_STATE_DISABLED`` and propagating changes to the hardware if this port is
disabled while being a bridge member
+Address databases
+-----------------
+
+Switching hardware is expected to have a table for FDB entries, however not all
+of them are active at the same time. An address database is the subset (partition)
+of FDB entries that is active (can be matched by address learning on RX, or FDB
+lookup on TX) depending on the state of the port. An address database may
+occasionally be called "FID" (Filtering ID) in this document, although the
+underlying implementation may choose whatever is available to the hardware.
+
+For example, all ports that belong to a VLAN-unaware bridge (which is
+*currently* VLAN-unaware) are expected to learn source addresses in the
+database associated by the driver with that bridge (and not with other
+VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a
+VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having
+the same MAC DA as the packet, which is present on another port member of the
+same bridge. At the same time, the FDB lookup process must be able to not find
+an FDB entry having the same MAC DA as the packet, if that entry points towards
+a port which is a member of a different VLAN-unaware bridge (and is therefore
+associated with a different address database).
+
+Similarly, each VLAN of each offloaded VLAN-aware bridge should have an
+associated address database, which is shared by all ports which are members of
+that VLAN, but not shared by ports belonging to different bridges that are
+members of the same VID.
+
+In this context, a VLAN-unaware database means that all packets are expected to
+match on it irrespective of VLAN ID (only MAC address lookup), whereas a
+VLAN-aware database means that packets are supposed to match based on the VLAN
+ID from the classified 802.1Q header (or the pvid if untagged).
+
+At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0,
+whereas VLAN-aware FDB entries have non-zero VID values. Note that a
+VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a
+VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the
+software bridge keeps separate address databases, and offloads to hardware the
+FDB entries belonging to these databases, through switchdev, asynchronously
+relative to the moment when the databases become active or inactive.
+
+When a user port operates in standalone mode, its driver should configure it to
+use a separate database called a port private database. This is different from
+the databases described above, and should impede operation as standalone port
+(packet in, packet out to the CPU port) as little as possible. For example,
+on ingress, it should not attempt to learn the MAC SA of ingress traffic, since
+learning is a bridging layer service and this is a standalone port, therefore
+it would consume useless space. With no address learning, the port private
+database should be empty in a naive implementation, and in this case, all
+received packets should be trivially flooded to the CPU port.
+
+DSA (cascade) and CPU ports are also called "shared" ports because they service
+multiple address databases, and the database that a packet should be associated
+to is usually embedded in the DSA tag. This means that the CPU port may
+simultaneously transport packets coming from a standalone port (which were
+classified by hardware in one address database), and from a bridge port (which
+were classified to a different address database).
+
+Switch drivers which satisfy certain criteria are able to optimize the naive
+configuration by removing the CPU port from the flooding domain of the switch,
+and just program the hardware with FDB entries pointing towards the CPU port
+for which it is known that software is interested in those MAC addresses.
+Packets which do not match a known FDB entry will not be delivered to the CPU,
+which will save CPU cycles required for creating an skb just to drop it.
+
+DSA is able to perform host address filtering for the following kinds of
+addresses:
+
+- Primary unicast MAC addresses of ports (``dev->dev_addr``). These are
+ associated with the port private database of the respective user port,
+ and the driver is notified to install them through ``port_fdb_add`` towards
+ the CPU port.
+
+- Secondary unicast and multicast MAC addresses of ports (addresses added
+ through ``dev_uc_add()`` and ``dev_mc_add()``). These are also associated
+ with the port private database of the respective user port.
+
+- Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC
+ addresses of the bridge ports, for which packets must be terminated locally
+ and not forwarded. They are associated with the address database for that
+ bridge.
+
+- Static bridge FDB entries installed towards foreign (non-DSA) interfaces
+ present in the same bridge as some DSA switch ports. These are also
+ associated with the address database for that bridge.
+
+- Dynamically learned FDB entries on foreign interfaces present in the same
+ bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port``
+ is set to true by the driver. These are associated with the address database
+ for that bridge.
+
+For various operations detailed below, DSA provides a ``dsa_db`` structure
+which can be of the following types:
+
+- ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to
+ the port private database of user port ``db->dp``.
+- ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge
+ ``db->bridge``. Separation between the VLAN-unaware database and the per-VID
+ databases of this bridge is expected to be done by the driver.
+- ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``.
+ Note: ``DSA_DB_LAG`` is currently unused and may be removed in the future.
+
+The drivers which act upon the ``dsa_db`` argument in ``port_fdb_add``,
+``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true.
+
+DSA associates each offloaded bridge and each offloaded LAG with a one-based ID
+(``struct dsa_bridge :: num``, ``struct dsa_lag :: id``) for the purposes of
+refcounting addresses on shared ports. Drivers may piggyback on DSA's numbering
+scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may
+implement their own.
+
+Only the drivers which declare support for FDB isolation are notified of FDB
+entries on the CPU port belonging to ``DSA_DB_PORT`` databases.
+For compatibility/legacy reasons, ``DSA_DB_BRIDGE`` addresses are notified to
+drivers even if they do not support FDB isolation. However, ``db->bridge.num``
+and ``db->lag.id`` are always set to 0 in that case (to denote the lack of
+isolation, for refcounting purposes).
+
+Note that it is not mandatory for a switch driver to implement physically
+separate address databases for each standalone user port. Since FDB entries in
+the port private databases will always point to the CPU port, there is no risk
+for incorrect forwarding decisions. In this case, all standalone ports may
+share the same database, but the reference counting of host-filtered addresses
+(not deleting the FDB entry for a port's MAC address if it's still in use by
+another port) becomes the responsibility of the driver, because DSA is unaware
+that the port databases are in fact shared. This can be achieved by calling
+``dsa_fdb_present_in_other_db()`` and ``dsa_mdb_present_in_other_db()``.
+The down side is that the RX filtering lists of each user port are in fact
+shared, which means that user port A may accept a packet with a MAC DA it
+shouldn't have, only because that MAC address was in the RX filtering list of
+user port B. These packets will still be dropped in software, however.
+
Bridge layer
------------
function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to
a software implementation.
-.. note:: VLAN ID 0 corresponds to the port private database, which, in the context
- of DSA, would be its port-based VLAN, used by the associated bridge device.
-
- ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a
Forwarding Database entry, the switch hardware should be programmed to delete
the specified MAC address from the specified VLAN ID if it was mapped into
specified address in the specified VLAN ID in the forwarding database
associated with this VLAN ID.
-.. note:: VLAN ID 0 corresponds to the port private database, which, in the context
- of DSA, would be its port-based VLAN, used by the associated bridge device.
-
- ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a
multicast database entry, the switch hardware should be programmed to delete
the specified MAC address from the specified VLAN ID if it was mapped into
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