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Documentation: networking: dsa: add paragraph for the LAG offload 

Add a short summary of the methods that a driver writer must implement
for offloading a link aggregation group, and what is still missing.

Cc: Tobias Waldekranz <tobias@waldekranz.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Tobias Waldekranz <tobias@waldekranz.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vladimir Oltean 2021-03-16 13:24:15 +02:00 committed by David S. Miller
parent 8411abbcad
commit a9985444f2
1 changed files with 33 additions and 0 deletions
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33
Documentation/networking/dsa/dsa.rst
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@ -724,6 +724,39 @@ Bridge VLAN filtering
function that the driver has to call for each MAC address known to be behind
the given port. A switchdev object is used to carry the VID and MDB info.
Link aggregation
----------------
Link aggregation is implemented in the Linux networking stack by the bonding
and team drivers, which are modeled as virtual, stackable network interfaces.
DSA is capable of offloading a link aggregation group (LAG) to hardware that
supports the feature, and supports bridging between physical ports and LAGs,
as well as between LAGs. A bonding/team interface which holds multiple physical
ports constitutes a logical port, although DSA has no explicit concept of a
logical port at the moment. Due to this, events where a LAG joins/leaves a
bridge are treated as if all individual physical ports that are members of that
LAG join/leave the bridge. Switchdev port attributes (VLAN filtering, STP
state, etc) and objects (VLANs, MDB entries) offloaded to a LAG as bridge port
are treated similarly: DSA offloads the same switchdev object / port attribute
on all members of the LAG. Static bridge FDB entries on a LAG are not yet
supported, since the DSA driver API does not have the concept of a logical port
ID.
- ``port_lag_join``: function invoked when a given switch port is added to a
LAG. The driver may return ``-EOPNOTSUPP``, and in this case, DSA will fall
back to a software implementation where all traffic from this port is sent to
the CPU.
- ``port_lag_leave``: function invoked when a given switch port leaves a LAG
and returns to operation as a standalone port.
- ``port_lag_change``: function invoked when the link state of any member of
the LAG changes, and the hashing function needs rebalancing to only make use
of the subset of physical LAG member ports that are up.
Drivers that benefit from having an ID associated with each offloaded LAG
can optionally populate ``ds->num_lag_ids`` from the ``dsa_switch_ops::setup``
method. The LAG ID associated with a bonding/team interface can then be
retrieved by a DSA switch driver using the ``dsa_lag_id`` function.
TODO
====