[PATCH 3/3] net: pse-pd: add lazy PSE control resolution for modular drivers

[Carlo Szelinsky <github@szelinsky.de>]

When a PSE controller driver is built as a module and was not probed
during PHY registration, the PHY ends up with psec=NULL. Add
pse_control_try_resolve() to lazily resolve the PSE control on first
ethtool access.

Call pse_control_try_resolve() in both the GET and SET ethtool PSE
handlers, before checking phydev->psec. The function is serialized by
RTNL (enforced via ASSERT_RTNL), preventing concurrent callers from
double-allocating a PSE control.

If resolution fails (e.g. the module still has not loaded), a debug
message is emitted via phydev_dbg() and the handler falls through to
the existing "No PSE is attached" error path.

Signed-off-by: Carlo Szelinsky <github@szelinsky.de>
---
 drivers/net/pse-pd/pse_core.c | 36 +++++++++++++++++++++++++++++++++++
 include/linux/pse-pd/pse.h    |  5 +++++
 net/ethtool/pse-pd.c          |  4 ++++
 3 files changed, 45 insertions(+)

diff --git a/drivers/net/pse-pd/pse_core.c b/drivers/net/pse-pd/pse_core.c
index 566b07c336bf..390df23a991c 100644
--- a/drivers/net/pse-pd/pse_core.c
+++ b/drivers/net/pse-pd/pse_core.c
@@ -1569,6 +1569,42 @@ struct pse_control *of_pse_control_get(struct device_node *node,
 }
 EXPORT_SYMBOL_GPL(of_pse_control_get);
 
+/**
+ * pse_control_try_resolve - attempt to resolve a deferred PSE control
+ * @phydev: the PHY device whose PSE control may need resolution
+ *
+ * When a PSE controller driver is built as a module, it may not have
+ * probed when PHYs were registered on the MDIO bus. This function
+ * retries PSE control acquisition and should be called before
+ * accessing phydev->psec in ethtool handlers.
+ *
+ * Context: Caller must hold RTNL.
+ */
+void pse_control_try_resolve(struct phy_device *phydev)
+{
+	struct device_node *np;
+	struct pse_control *psec;
+
+	ASSERT_RTNL();
+
+	if (phydev->psec)
+		return;
+
+	np = phydev->mdio.dev.of_node;
+	if (!np || !of_property_present(np, "pses"))
+		return;
+
+	psec = of_pse_control_get(np, phydev);
+	if (IS_ERR(psec)) {
+		phydev_dbg(phydev, "failed to resolve PSE control: %pe\n",
+			   psec);
+		return;
+	}
+
+	phydev->psec = psec;
+}
+EXPORT_SYMBOL_GPL(pse_control_try_resolve);
+
 /**
  * pse_get_sw_admin_state - Convert the software admin state to c33 or podl
  *			    admin state value used in the standard
diff --git a/include/linux/pse-pd/pse.h b/include/linux/pse-pd/pse.h
index b86cce740551..d2f9b7c1acdf 100644
--- a/include/linux/pse-pd/pse.h
+++ b/include/linux/pse-pd/pse.h
@@ -350,6 +350,7 @@ int devm_pse_irq_helper(struct pse_controller_dev *pcdev, int irq,
 struct pse_control *of_pse_control_get(struct device_node *node,
 				       struct phy_device *phydev);
 void pse_control_put(struct pse_control *psec);
+void pse_control_try_resolve(struct phy_device *phydev);
 
 int pse_ethtool_get_status(struct pse_control *psec,
 			   struct netlink_ext_ack *extack,
@@ -379,6 +380,10 @@ static inline void pse_control_put(struct pse_control *psec)
 {
 }
 
+static inline void pse_control_try_resolve(struct phy_device *phydev)
+{
+}
+
 static inline int pse_ethtool_get_status(struct pse_control *psec,
 					 struct netlink_ext_ack *extack,
 					 struct ethtool_pse_control_status *status)
diff --git a/net/ethtool/pse-pd.c b/net/ethtool/pse-pd.c
index 2eb9bdc2dcb9..adffc230acd6 100644
--- a/net/ethtool/pse-pd.c
+++ b/net/ethtool/pse-pd.c
@@ -42,6 +42,8 @@ static int pse_get_pse_attributes(struct phy_device *phydev,
 		return -EOPNOTSUPP;
 	}
 
+	pse_control_try_resolve(phydev);
+
 	if (!phydev->psec) {
 		NL_SET_ERR_MSG(extack, "No PSE is attached");
 		return -EOPNOTSUPP;
@@ -249,6 +251,8 @@ ethnl_set_pse_validate(struct phy_device *phydev, struct genl_info *info)
 		return -EOPNOTSUPP;
 	}
 
+	pse_control_try_resolve(phydev);
+
 	if (!phydev->psec) {
 		NL_SET_ERR_MSG(info->extack, "No PSE is attached");
 		return -EOPNOTSUPP;
-- 
2.43.0