netdev - [RFC PATCH net-next 08/12] Documentation: networking: dsa: add paragraph for the LAG offload

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Message-Id: <20210221213355.1241450-9-olteanv@gmail.com>
Date:   Sun, 21 Feb 2021 23:33:51 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ido Schimmel <idosch@...sch.org>,
        DENG Qingfang <dqfext@...il.com>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        George McCollister <george.mccollister@...il.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: [RFC PATCH net-next 08/12] Documentation: networking: dsa: add paragraph for the LAG offload

From: Vladimir Oltean <vladimir.oltean@....com>

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@...dekranz.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 Documentation/networking/dsa/dsa.rst | 32 ++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Documentation/networking/dsa/dsa.rst b/Documentation/networking/dsa/dsa.rst
index 463b48714fe9..0a5b06cf4d45 100644
--- a/Documentation/networking/dsa/dsa.rst
+++ b/Documentation/networking/dsa/dsa.rst
@@ -698,6 +698,38 @@ 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
+physical 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) on a LAG are treated similarly: DSA offloads the same switchdev
+port attribute on all members of the LAG. Switchdev objects on a LAG (FDB, MDB)
+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 only towards 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
 ====
 
-- 
2.25.1