net: phylib: add link_change_notify callback to phy device

Add a notify callback to inform phy drivers when the core is about to
do its link adjustment. No change for drivers that do not implement
this callback.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy.c

@@ -720,6 +720,9 @@ void phy_state_machine(struct work_struct *work)
 
 	mutex_lock(&phydev->lock);
 
+	if (phydev->drv->link_change_notify)
+		phydev->drv->link_change_notify(phydev);
+
 	switch (phydev->state) {
 	case PHY_DOWN:
 	case PHY_STARTING:

include/linux/phy.h

@@ -536,6 +536,15 @@ struct phy_driver {
 	/* See set_wol, but for checking whether Wake on LAN is enabled. */
 	void (*get_wol)(struct phy_device *dev, struct ethtool_wolinfo *wol);
 
+	/*
+	 * Called to inform a PHY device driver when the core is about to
+	 * change the link state. This callback is supposed to be used as
+	 * fixup hook for drivers that need to take action when the link
+	 * state changes. Drivers are by no means allowed to mess with the
+	 * PHY device structure in their implementations.
+	 */
+	void (*link_change_notify)(struct phy_device *dev);
+
 	struct device_driver driver;
 };
 #define to_phy_driver(d) container_of(d, struct phy_driver, driver)