net: phy: avoid unneeded MDIO reads in genphy_read_status

Considering that in polling mode each link drop will be latched,
settings can't have changed if link was up and is up.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy_device.c

@@ -1739,13 +1739,17 @@ EXPORT_SYMBOL(genphy_update_link);
  */
 int genphy_read_status(struct phy_device *phydev)
 {
-	int adv, lpa, lpagb, err;
+	int adv, lpa, lpagb, err, old_link = phydev->link;
 
 	/* Update the link, but return if there was an error */
 	err = genphy_update_link(phydev);
 	if (err)
 		return err;
 
+	/* why bother the PHY if nothing can have changed */
+	if (phydev->autoneg == AUTONEG_ENABLE && old_link && phydev->link)
+		return 0;
+
 	phydev->speed = SPEED_UNKNOWN;
 	phydev->duplex = DUPLEX_UNKNOWN;
 	phydev->pause = 0;