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docs: net: dsa: remove port_bridge_tx_fwd_offload

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We've changed the API through which we can offload the bridge TX
forwarding process. Update the documentation in light of the removal of
2 DSA switch ops.

Fixes: b079922ba2 ("net: dsa: add a "tx_fwd_offload" argument to ->port_bridge_join")
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>
This commit is contained in:
Vladimir Oltean 2022-07-16 21:53:38 +03:00 committed by David S. Miller
parent 0cb8682ebf
commit 3083623948
1 changed files with 46 additions and 16 deletions
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62
Documentation/networking/dsa/dsa.rst
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@ -730,10 +730,56 @@ Power management
Bridge layer
------------
Offloading the bridge forwarding plane is optional and handled by the methods
below. They may be absent, return -EOPNOTSUPP, or ``ds->max_num_bridges`` may
be non-zero and exceeded, and in this case, joining a bridge port is still
possible, but the packet forwarding will take place in software, and the ports
under a software bridge must remain configured in the same way as for
standalone operation, i.e. have all bridging service functions (address
learning etc) disabled, and send all received packets to the CPU port only.
Concretely, a port starts offloading the forwarding plane of a bridge once it
returns success to the ``port_bridge_join`` method, and stops doing so after
``port_bridge_leave`` has been called. Offloading the bridge means autonomously
learning FDB entries in accordance with the software bridge port's state, and
autonomously forwarding (or flooding) received packets without CPU intervention.
This is optional even when offloading a bridge port. Tagging protocol drivers
are expected to call ``dsa_default_offload_fwd_mark(skb)`` for packets which
have already been autonomously forwarded in the forwarding domain of the
ingress switch port. DSA, through ``dsa_port_devlink_setup()``, considers all
switch ports part of the same tree ID to be part of the same bridge forwarding
domain (capable of autonomous forwarding to each other).
Offloading the TX forwarding process of a bridge is a distinct concept from
simply offloading its forwarding plane, and refers to the ability of certain
driver and tag protocol combinations to transmit a single skb coming from the
bridge device's transmit function to potentially multiple egress ports (and
thereby avoid its cloning in software).
Packets for which the bridge requests this behavior are called data plane
packets and have ``skb->offload_fwd_mark`` set to true in the tag protocol
driver's ``xmit`` function. Data plane packets are subject to FDB lookup,
hardware learning on the CPU port, and do not override the port STP state.
Additionally, replication of data plane packets (multicast, flooding) is
handled in hardware and the bridge driver will transmit a single skb for each
packet that may or may not need replication.
When the TX forwarding offload is enabled, the tag protocol driver is
responsible to inject packets into the data plane of the hardware towards the
correct bridging domain (FID) that the port is a part of. The port may be
VLAN-unaware, and in this case the FID must be equal to the FID used by the
driver for its VLAN-unaware address database associated with that bridge.
Alternatively, the bridge may be VLAN-aware, and in that case, it is guaranteed
that the packet is also VLAN-tagged with the VLAN ID that the bridge processed
this packet in. It is the responsibility of the hardware to untag the VID on
the egress-untagged ports, or keep the tag on the egress-tagged ones.
- ``port_bridge_join``: bridge layer function invoked when a given switch port is
added to a bridge, this function should do what's necessary at the switch
level to permit the joining port to be added to the relevant logical
domain for it to ingress/egress traffic with other members of the bridge.
By setting the ``tx_fwd_offload`` argument to true, the TX forwarding process
of this bridge is also offloaded.
- ``port_bridge_leave``: bridge layer function invoked when a given switch port is
removed from a bridge, this function should do what's necessary at the
@ -755,22 +801,6 @@ Bridge layer
CPU port, and flooding towards the CPU port should also be enabled, due to a
lack of an explicit address filtering mechanism in the DSA core.
- ``port_bridge_tx_fwd_offload``: bridge layer function invoked after
``port_bridge_join`` when a driver sets ``ds->num_fwd_offloading_bridges`` to
a non-zero value. Returning success in this function activates the TX
forwarding offload bridge feature for this port, which enables the tagging
protocol driver to inject data plane packets towards the bridging domain that
the port is a part of. Data plane packets are subject to FDB lookup, hardware
learning on the CPU port, and do not override the port STP state.
Additionally, replication of data plane packets (multicast, flooding) is
handled in hardware and the bridge driver will transmit a single skb for each
packet that needs replication. The method is provided as a configuration
point for drivers that need to configure the hardware for enabling this
feature.
- ``port_bridge_tx_fwd_unoffload``: bridge layer function invoked when a driver
leaves a bridge port which had the TX forwarding offload feature enabled.
- ``port_fast_age``: bridge layer function invoked when flushing the
dynamically learned FDB entries on the port is necessary. This is called when
transitioning from an STP state where learning should take place to an STP