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Date:   Tue, 15 Dec 2020 17:00:56 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Saeed Mahameed <saeed@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jason Gunthorpe <jgg@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, David Ahern <dsahern@...nel.org>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        david.m.ertman@...el.com, dan.j.williams@...el.com,
        kiran.patil@...el.com, gregkh@...uxfoundation.org,
        Parav Pandit <parav@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [net-next v5 14/15] devlink: Extend devlink port documentation
 for subfunctions

On Tue, 15 Dec 2020 01:03:57 -0800 Saeed Mahameed wrote:
> +Subfunctions are lightweight functions that has parent PCI function on which
> +it is deployed. Subfunctions are created and deployed in unit of 1. Unlike
> +SRIOV VFs, they don't require their own PCI virtual function. They communicate
> +with the hardware through the parent PCI function. Subfunctions can possibly
> +scale better.
> +
> +To use a subfunction, 3 steps setup sequence is followed.
> +(1) create - create a subfunction;
> +(2) configure - configure subfunction attributes;
> +(3) deploy - deploy the subfunction;
> +
> +Subfunction management is done using devlink port user interface.
> +User performs setup on the subfunction management device.
> +
> +(1) Create
> +----------
> +A subfunction is created using a devlink port interface. User adds the
> +subfunction by adding a devlink port of subfunction flavour. The devlink
> +kernel code calls down to subfunction management driver (devlink op) and asks
> +it to create a subfunction devlink port. Driver then instantiates the
> +subfunction port and any associated objects such as health reporters and
> +representor netdevice.
> +
> +(2) Configure
> +-------------
> +Subfunction devlink port is created but it is not active yet. That means the
> +entities are created on devlink side, the e-switch port representor is created,
> +but the subfunction device itself it not created. User might use e-switch port
> +representor to do settings, putting it into bridge, adding TC rules, etc. User
> +might as well configure the hardware address (such as MAC address) of the
> +subfunction while subfunction is inactive.
> +
> +(3) Deploy
> +----------
> +Once subfunction is configured, user must activate it to use it. Upon
> +activation, subfunction management driver asks the subfunction management
> +device to instantiate the actual subfunction device on particular PCI function.
> +A subfunction device is created on the :ref:`Documentation/driver-api/auxiliary_bus.rst <auxiliary_bus>`. At this point matching
> +subfunction driver binds to the subfunction's auxiliary device.
> +
> +Terms and Definitions
> +=====================
> +
> +.. list-table:: Terms and Definitions
> +   :widths: 22 90
> +
> +   * - Term
> +     - Definitions
> +   * - ``PCI device``
> +     - A physical PCI device having one or more PCI bus consists of one or
> +       more PCI controllers.
> +   * - ``PCI controller``
> +     -  A controller consists of potentially multiple physical functions,
> +        virtual functions and subfunctions.
> +   * - ``Port function``
> +     -  An object to manage the function of a port.
> +   * - ``Subfunction``
> +     -  A lightweight function that has parent PCI function on which it is
> +        deployed.
> +   * - ``Subfunction device``
> +     -  A bus device of the subfunction, usually on a auxiliary bus.
> +   * - ``Subfunction driver``
> +     -  A device driver for the subfunction auxiliary device.
> +   * - ``Subfunction management device``
> +     -  A PCI physical function that supports subfunction management.
> +   * - ``Subfunction management driver``
> +     -  A device driver for PCI physical function that supports
> +        subfunction management using devlink port interface.
> +   * - ``Subfunction host driver``
> +     -  A device driver for PCI physical function that host subfunction
> +        devices. In most cases it is same as subfunction management driver. When
> +        subfunction is used on external controller, subfunction management and
> +        host drivers are different.

Would be great if someone from Mellanox could proof read this before we
spend cycles on correcting spelling in public review.

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