docs: net: dsa: delete misinformation about -EOPNOTSUPP for FDB/MDB/VLAN

Returning -EOPNOTSUPP does *NOT* mean anything special.

port_vlan_add() is actually called from 2 code paths, one is
vlan_vid_add() from 8021q module and the other is
br_switchdev_port_vlan_add() from switchdev.

The bridge has a wrapper __vlan_vid_add() which first tries via
switchdev, then if that returns -EOPNOTSUPP, tries again via the VLAN RX
filters in the 8021q module. But DSA doesn't distinguish between one
call path and the other when calling the driver's port_vlan_add(), so if
the driver returns -EOPNOTSUPP to switchdev, it also returns -EOPNOTSUPP
to the 8021q module. And the latter is a hard error.

port_fdb_add() is called from the deferred dsa_owq only, so obviously
its return code isn't propagated anywhere, and cannot be interpreted in
any way.

The return code from port_mdb_add() is propagated to the bridge, but
again, this doesn't do anything special when -EOPNOTSUPP is returned,
but rather, br_switchdev_mdb_notify() returns void.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/dsa/dsa.rst

@@ -951,19 +951,15 @@ Bridge VLAN filtering
   allowed.
 
 - ``port_vlan_add``: bridge layer function invoked when a VLAN is configured
-  (tagged or untagged) for the given switch port. If the operation is not
-  supported by the hardware, this function should return ``-EOPNOTSUPP`` to
-  inform the bridge code to fallback to a software implementation.
+  (tagged or untagged) for the given switch port..
 
 - ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the
   given switch port
 
 - ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a
   Forwarding Database entry, the switch hardware should be programmed with the
   specified address in the specified VLAN Id in the forwarding database
-  associated with this VLAN ID. If the operation is not supported, this
-  function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to
-  a software implementation.
+  associated with this VLAN ID.
 
 - ``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
@@ -978,9 +974,7 @@ Bridge VLAN filtering
   the ``bridge fdb show`` command.
 
 - ``port_mdb_add``: bridge layer function invoked when the bridge wants to install
-  a multicast database entry. If the operation is not supported, this function
-  should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to a
-  software implementation. The switch hardware should be programmed with the
+  a multicast database entry. The switch hardware should be programmed with the
   specified address in the specified VLAN ID in the forwarding database
   associated with this VLAN ID.