Documentation: Add documentation for eswitch attribute

Provide devlink documentation for three eswitch attributes:
mode, inline-mode, and encap-mode.
Signed-off-by: William Tu <witu@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20240325181228.6244-1-witu@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/devlink/devlink-eswitch-attr.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+Devlink E-Switch Attribute
+==========================
+
+Devlink E-Switch supports two modes of operation: legacy and switchdev.
+Legacy mode operates based on traditional MAC/VLAN steering rules. Switching
+decisions are made based on MAC addresses, VLANs, etc. There is limited ability
+to offload switching rules to hardware.
+
+On the other hand, switchdev mode allows for more advanced offloading
+capabilities of the E-Switch to hardware. In switchdev mode, more switching
+rules and logic can be offloaded to the hardware switch ASIC. It enables
+representor netdevices that represent the slow path of virtual functions (VFs)
+or scalable-functions (SFs) of the device. See more information about
+:ref:`Documentation/networking/switchdev.rst <switchdev>` and
+:ref:`Documentation/networking/representors.rst <representors>`.
+
+In addition, the devlink E-Switch also comes with other attributes listed
+in the following section.
+
+Attributes Description
+======================
+
+The following is a list of E-Switch attributes.
+
+.. list-table:: E-Switch attributes
+   :widths: 8 5 45
+
+   * - Name
+     - Type
+     - Description
+   * - ``mode``
+     - enum
+     - The mode of the device. The mode can be one of the following:
+
+       * ``legacy`` operates based on traditional MAC/VLAN steering
+         rules.
+       * ``switchdev`` allows for more advanced offloading capabilities of
+         the E-Switch to hardware.
+   * - ``inline-mode``
+     - enum
+     - Some HWs need the VF driver to put part of the packet
+       headers on the TX descriptor so the e-switch can do proper
+       matching and steering. Support for both switchdev mode and legacy mode.
+
+       * ``none`` none.
+       * ``link`` L2 mode.
+       * ``network`` L3 mode.
+       * ``transport`` L4 mode.
+   * - ``encap-mode``
+     - enum
+     - The encapsulation mode of the device. Support for both switchdev mode
+       and legacy mode. The mode can be one of the following:
+
+       * ``none`` Disable encapsulation support.
+       * ``basic`` Enable encapsulation support.
+
+Example Usage
+=============
+
+.. code:: shell
+
+    # enable switchdev mode
+    $ devlink dev eswitch set pci/0000:08:00.0 mode switchdev
+
+    # set inline-mode and encap-mode
+    $ devlink dev eswitch set pci/0000:08:00.0 inline-mode none encap-mode basic
+
+    # display devlink device eswitch attributes
+    $ devlink dev eswitch show pci/0000:08:00.0
+      pci/0000:08:00.0: mode switchdev inline-mode none encap-mode basic
+
+    # enable encap-mode with legacy mode
+    $ devlink dev eswitch set pci/0000:08:00.0 mode legacy inline-mode none encap-mode basic

Documentation/networking/devlink/index.rst

@@ -67,6 +67,7 @@ general.
    devlink-selftests
    devlink-trap
    devlink-linecard
+   devlink-eswitch-attr
 
 Driver-specific documentation
 -----------------------------

Documentation/networking/representors.rst

 .. SPDX-License-Identifier: GPL-2.0
+.. _representors:
 
 =============================
 Network Function Representors