net: phy: Introduce generic SFP handling for PHY drivers

There are currently 4 PHY drivers that can drive downstream SFPs:
marvell.c, marvell10g.c, at803x.c and marvell-88x2222.c. Most of the
logic is boilerplate, either calling into generic phylib helpers (for
SFP PHY attach, bus attach, etc.) or performing the same tasks with a
bit of validation :
 - Getting the module's expected interface mode
 - Making sure the PHY supports it
 - Optionaly perform some configuration to make sure the PHY outputs
   the right mode

This can be made more generic by leveraging the phy_port, and its
configure_mii() callback which allows setting a port's interfaces when
the port is a serdes.

Introduce a generic PHY SFP support. If a driver doesn't probe the SFP
bus itself, but an SFP phandle is found in devicetree/firmware, then the
generic PHY SFP support will be used, relying on port ops.

PHY driver need to :
 - Register a .attach_port() callback
 - When a serdes port is registered to the PHY, drivers must set
   port->interfaces to the set of PHY_INTERFACE_MODE the port can output
 - If the port has limitations regarding speed, duplex and aneg, the
   port can also fine-tune the final linkmodes that can be supported
 - The port may register a set of ops, including .configure_mii(), that
   will be called at module_insert time to adjust the interface based on
   the module detected.

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260108080041.553250-8-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phy_device.c

@@ -1598,6 +1598,86 @@ void phy_sfp_detach(void *upstream, struct sfp_bus *bus)
 }
 EXPORT_SYMBOL(phy_sfp_detach);
 
+static int phy_sfp_module_insert(void *upstream, const struct sfp_eeprom_id *id)
+{
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(sfp_support);
+	struct phy_device *phydev = upstream;
+	const struct sfp_module_caps *caps;
+	struct phy_port *port;
+
+	phy_interface_t iface;
+
+	linkmode_zero(sfp_support);
+
+	port = phy_get_sfp_port(phydev);
+	if (!port)
+		return -EINVAL;
+
+	caps = sfp_get_module_caps(phydev->sfp_bus);
+
+	linkmode_and(sfp_support, port->supported, caps->link_modes);
+	if (linkmode_empty(sfp_support)) {
+		dev_err(&phydev->mdio.dev, "incompatible SFP module inserted, no common linkmode\n");
+		return -EINVAL;
+	}
+
+	iface = sfp_select_interface(phydev->sfp_bus, sfp_support);
+	if (iface == PHY_INTERFACE_MODE_NA) {
+		dev_err(&phydev->mdio.dev, "PHY %s does not support the SFP module's requested MII interfaces\n",
+			phydev_name(phydev));
+		return -EINVAL;
+	}
+
+	if (phydev->n_ports == 1)
+		phydev->port = caps->port;
+
+	if (port->ops && port->ops->configure_mii)
+		return port->ops->configure_mii(port, true, iface);
+
+	return 0;
+}
+
+static void phy_sfp_module_remove(void *upstream)
+{
+	struct phy_device *phydev = upstream;
+	struct phy_port *port = phy_get_sfp_port(phydev);
+
+	if (port && port->ops && port->ops->configure_mii)
+		port->ops->configure_mii(port, false, PHY_INTERFACE_MODE_NA);
+
+	if (phydev->n_ports == 1)
+		phydev->port = PORT_NONE;
+}
+
+static void phy_sfp_link_up(void *upstream)
+{
+	struct phy_device *phydev = upstream;
+	struct phy_port *port = phy_get_sfp_port(phydev);
+
+	if (port && port->ops && port->ops->link_up)
+		port->ops->link_up(port);
+}
+
+static void phy_sfp_link_down(void *upstream)
+{
+	struct phy_device *phydev = upstream;
+	struct phy_port *port = phy_get_sfp_port(phydev);
+
+	if (port && port->ops && port->ops->link_down)
+		port->ops->link_down(port);
+}
+
+static const struct sfp_upstream_ops sfp_phydev_ops = {
+	.attach = phy_sfp_attach,
+	.detach = phy_sfp_detach,
+	.module_insert = phy_sfp_module_insert,
+	.module_remove = phy_sfp_module_remove,
+	.link_up = phy_sfp_link_up,
+	.link_down = phy_sfp_link_down,
+	.connect_phy = phy_sfp_connect_phy,
+	.disconnect_phy = phy_sfp_disconnect_phy,
+};
+
 static int phy_add_port(struct phy_device *phydev, struct phy_port *port)
 {
 	int ret = 0;
@@ -1658,6 +1738,7 @@ static int phy_setup_sfp_port(struct phy_device *phydev)
 	 * is a MII port.
 	 */
 	port->is_mii = true;
+	port->is_sfp = true;
 
 	/* The port->supported and port->interfaces list will be populated
 	 * when attaching the port to the phydev.
@@ -3505,6 +3586,13 @@ static int phy_setup_ports(struct phy_device *phydev)
 	if (ret)
 		return ret;
 
+	/* Use generic SFP probing only if the driver didn't do so already */
+	if (!phydev->sfp_bus) {
+		ret = phy_sfp_probe(phydev, &sfp_phydev_ops);
+		if (ret)
+			goto out;
+	}
+
 	if (phydev->n_ports < phydev->max_n_ports) {
 		ret = phy_default_setup_single_port(phydev);
 		if (ret)
@@ -3540,6 +3628,25 @@ static int phy_setup_ports(struct phy_device *phydev)
 	return ret;
 }
 
+/**
+ * phy_get_sfp_port() - Returns the first valid SFP port of a PHY
+ * @phydev: pointer to the PHY device to get the SFP port from
+ *
+ * Returns: The first active SFP (serdes) port of a PHY device, NULL if none
+ * exist.
+ */
+struct phy_port *phy_get_sfp_port(struct phy_device *phydev)
+{
+	struct phy_port *port;
+
+	list_for_each_entry(port, &phydev->ports, head)
+		if (port->active && port->is_sfp)
+			return port;
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(phy_get_sfp_port);
+
 /**
  * fwnode_mdio_find_device - Given a fwnode, find the mdio_device
  * @fwnode: pointer to the mdio_device's fwnode

include/linux/phy.h

@@ -2455,6 +2455,8 @@ int __phy_hwtstamp_set(struct phy_device *phydev,
 		       struct kernel_hwtstamp_config *config,
 		       struct netlink_ext_ack *extack);
 
+struct phy_port *phy_get_sfp_port(struct phy_device *phydev);
+
 extern const struct bus_type mdio_bus_type;
 extern const struct class mdio_bus_class;
 

include/linux/phy_port.h

@@ -49,6 +49,7 @@ struct phy_port_ops {
  * @active: Indicates if the port is currently part of the active link.
  * @is_mii: Indicates if this port is MII (Media Independent Interface),
  *          or MDI (Media Dependent Interface).
+ * @is_sfp: Indicates if this port drives an SFP cage.
  */
 struct phy_port {
 	struct list_head head;
@@ -67,6 +68,7 @@ struct phy_port {
 	unsigned int not_described:1;
 	unsigned int active:1;
 	unsigned int is_mii:1;
+	unsigned int is_sfp:1;
 };
 
 struct phy_port *phy_port_alloc(void);