[PATCH net-next v3 1/2] doc: sfp-phylink: update the porting guide with PCS handling

From: Maxime Chevallier
Date: Fri Mar 01 2024 - 11:49:54 EST


Now that phylink has a comprehensive PCS support, update the porting
guide to explain the process of supporting the PCS configuration. This
also removed outdated references to phylink_config fields that no longer
exists.

Signed-off-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
---
V3: Remove stray whitespace and wrap a long line
V2: Squash both V1 patches together to create this one.

Documentation/networking/sfp-phylink.rst | 147 ++++++++++++++++++++---
1 file changed, 133 insertions(+), 14 deletions(-)

diff --git a/Documentation/networking/sfp-phylink.rst b/Documentation/networking/sfp-phylink.rst
index 8054d33f449f..5bf285d73e8a 100644
--- a/Documentation/networking/sfp-phylink.rst
+++ b/Documentation/networking/sfp-phylink.rst
@@ -231,16 +231,136 @@ this documentation.
For further information on these methods, please see the inline
documentation in :c:type:`struct phylink_mac_ops <phylink_mac_ops>`.

-9. Remove calls to of_parse_phandle() for the PHY,
- of_phy_register_fixed_link() for fixed links etc. from the probe
- function, and replace with:
+9. Fill-in the :c:type:`struct phylink_config <phylink_config>` fields with
+ a reference to the :c:type:`struct device <device>` associated to your
+ :c:type:`struct net_device <net_device>`:

.. code-block:: c

- struct phylink *phylink;
priv->phylink_config.dev = &dev.dev;
priv->phylink_config.type = PHYLINK_NETDEV;

+ Fill-in the various speeds, pause and duplex modes your MAC can handle:
+
+ .. code-block:: c
+
+ priv->phylink_config.mac_capabilities = MAC_SYM_PAUSE | MAC_10 | MAC_100 | MAC_1000FD;
+
+10. Some Ethernet controllers work in pair with a PCS (Physical Coding Sublayer)
+ block, that can handle among other things the encoding/decoding, link
+ establishment detection and autonegotiation. While some MACs have internal
+ PCS whose operation is transparent, some other require dedicated PCS
+ configuration for the link to become functional. In that case, phylink
+ provides a PCS abstraction through :c:type:`struct phylink_pcs <phylink_pcs>`.
+
+ Identify if your driver has one or more internal PCS blocks, and/or if
+ your controller can use an external PCS block that might be internally
+ connected to your controller.
+
+ If your controller doesn't have any internal PCS, you can go to step 11.
+
+ If your Ethernet controller contains one or several PCS blocks, create
+ one :c:type:`struct phylink_pcs <phylink_pcs>` instance per PCS block within
+ your driver's private data structure:
+
+ .. code-block:: c
+
+ struct phylink_pcs pcs;
+
+ Populate the relevant :c:type:`struct phylink_pcs_ops <phylink_pcs_ops>` to
+ configure your PCS. Create a :c:func:`pcs_get_state` function that reports
+ the inband link state, a :c:func:`pcs_config` function to configure your
+ PCS according to phylink-provided parameters, and a :c:func:`pcs_validate`
+ function that report to phylink all accepted configuration parameters for
+ your PCS:
+
+ .. code-block:: c
+
+ struct phylink_pcs_ops foo_pcs_ops = {
+ .pcs_validate = foo_pcs_validate,
+ .pcs_get_state = foo_pcs_get_state,
+ .pcs_config = foo_pcs_config,
+ };
+
+ Arrange for PCS link state interrupts to be forwarded into
+ phylink, via:
+
+ .. code-block:: c
+
+ phylink_pcs_change(pcs, link_is_up);
+
+ where ``link_is_up`` is true if the link is currently up or false
+ otherwise. If a PCS is unable to provide these interrupts, then
+ it should set ``pcs->pcs_poll = true;`` when creating the PCS.
+
+11. If your controller relies on, or accepts the presence of an external PCS
+ controlled through its own driver, add a pointer to a phylink_pcs instance
+ in your driver private data structure:
+
+ .. code-block:: c
+
+ struct phylink_pcs *pcs;
+
+ The way of getting an instance of the actual PCS depends on the platform,
+ some PCS sit on an MDIO bus and are grabbed by passing a pointer to the
+ corresponding :c:type:`struct mii_bus <mii_bus>` and the PCS's address on
+ that bus. In this example, we assume the controller attaches to a Lynx PCS
+ instance:
+
+ .. code-block:: c
+
+ priv->pcs = lynx_pcs_create_mdiodev(bus, 0);
+
+ Some PCS can be recovered based on firmware information:
+
+ .. code-block:: c
+
+ priv->pcs = lynx_pcs_create_fwnode(of_fwnode_handle(node));
+
+12. Populate the :c:func:`mac_select_pcs` callback and add it to your
+ :c:type:`struct phylink_mac_ops <phylink_mac_ops>` set of ops. This function
+ must return a pointer to the relevant :c:type:`struct phylink_pcs <phylink_pcs>`
+ that will be used for the requested link configuration:
+
+ .. code-block:: c
+
+ static struct phylink_pcs *foo_select_pcs(struct phylink_config *config,
+ phy_interface_t interface)
+ {
+ struct foo_priv *priv = container_of(config, struct foo_priv,
+ phylink_config);
+
+ if ( /* 'interface' needs a PCS to function */ )
+ return priv->pcs;
+
+ return NULL;
+ }
+
+ See :c:func:`mvpp2_select_pcs` for an example of a driver that has multiple
+ internal PCS.
+
+13. Fill-in all the :c:type:`phy_interface_t <phy_interface_t>` (i.e. all MAC to
+ PHY link modes) that your MAC can output. The following example shows a
+ configuration for a MAC that can handle all RGMII modes, SGMII and 1000BaseX.
+ You must adjust these according to what your MAC and all PCS associated
+ with this MAC are capable of, and not just the interface you wish to use:
+
+ .. code-block:: c
+
+ phy_interface_set_rgmii(priv->phylink_config.supported_interfaces);
+ __set_bit(PHY_INTERFACE_MODE_SGMII,
+ priv->phylink_config.supported_interfaces);
+ __set_bit(PHY_INTERFACE_MODE_1000BASEX,
+ priv->phylink_config.supported_interfaces);
+
+14. Remove calls to of_parse_phandle() for the PHY,
+ of_phy_register_fixed_link() for fixed links etc. from the probe
+ function, and replace with:
+
+ .. code-block:: c
+
+ struct phylink *phylink;
+
phylink = phylink_create(&priv->phylink_config, node, phy_mode, &phylink_ops);
if (IS_ERR(phylink)) {
err = PTR_ERR(phylink);
@@ -249,14 +369,14 @@ this documentation.

priv->phylink = phylink;

- and arrange to destroy the phylink in the probe failure path as
- appropriate and the removal path too by calling:
+ and arrange to destroy the phylink in the probe failure path as
+ appropriate and the removal path too by calling:

- .. code-block:: c
+ .. code-block:: c

phylink_destroy(priv->phylink);

-10. Arrange for MAC link state interrupts to be forwarded into
+15. Arrange for MAC link state interrupts to be forwarded into
phylink, via:

.. code-block:: c
@@ -264,17 +384,16 @@ this documentation.
phylink_mac_change(priv->phylink, link_is_up);

where ``link_is_up`` is true if the link is currently up or false
- otherwise. If a MAC is unable to provide these interrupts, then
- it should set ``priv->phylink_config.pcs_poll = true;`` in step 9.
+ otherwise.

-11. Verify that the driver does not call::
+16. Verify that the driver does not call::

netif_carrier_on()
netif_carrier_off()

- as these will interfere with phylink's tracking of the link state,
- and cause phylink to omit calls via the :c:func:`mac_link_up` and
- :c:func:`mac_link_down` methods.
+ as these will interfere with phylink's tracking of the link state,
+ and cause phylink to omit calls via the :c:func:`mac_link_up` and
+ :c:func:`mac_link_down` methods.

Network drivers should call phylink_stop() and phylink_start() via their
suspend/resume paths, which ensures that the appropriate
--
2.43.2