netdev - Re: [PATCH v2 net-next 08/12] Documentation: networking: dsa: add paragraph for the LAG offload

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Message-ID: <875z1rotyv.fsf@waldekranz.com>
Date:   Tue, 16 Mar 2021 19:04:56 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Vladimir Oltean <olteanv@...il.com>, 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>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH v2 net-next 08/12] Documentation: networking: dsa: add paragraph for the LAG offload

On Tue, Mar 16, 2021 at 13:24, Vladimir Oltean <olteanv@...il.com> wrote:
> 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>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> ---

Reviewed-by: Tobias Waldekranz <tobias@...dekranz.com>

>  Documentation/networking/dsa/dsa.rst | 33 ++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>
> diff --git a/Documentation/networking/dsa/dsa.rst b/Documentation/networking/dsa/dsa.rst
> index af604fe976b3..e8576e81735c 100644
> --- a/Documentation/networking/dsa/dsa.rst
> +++ b/Documentation/networking/dsa/dsa.rst
> @@ -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
>  ====
>  
> -- 
> 2.25.1