net: phy: add and use phy_check_downshift

So far PHY drivers have to check whether a downshift occurred to be
able to notify the user. To make life of drivers authors a little bit
easier move the downshift notification to phylib. phy_check_downshift()
compares the highest mutually advertised speed with the actual value
of phydev->speed (typically read by the PHY driver from a
vendor-specific register) to detect a downshift.

v2:
- Add downshift hint to phy_print_status
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy-core.c

@@ -329,6 +329,44 @@ void phy_resolve_aneg_linkmode(struct phy_device *phydev)
 }
 EXPORT_SYMBOL_GPL(phy_resolve_aneg_linkmode);
 
+/**
+ * phy_check_downshift - check whether downshift occurred
+ * @phydev: The phy_device struct
+ *
+ * Check whether a downshift to a lower speed occurred. If this should be the
+ * case warn the user.
+ * Prerequisite for detecting downshift is that PHY driver implements the
+ * read_status callback and sets phydev->speed to the actual link speed.
+ */
+void phy_check_downshift(struct phy_device *phydev)
+{
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(common);
+	int i, speed = SPEED_UNKNOWN;
+
+	phydev->downshifted_rate = 0;
+
+	if (phydev->autoneg == AUTONEG_DISABLE ||
+	    phydev->speed == SPEED_UNKNOWN)
+		return;
+
+	linkmode_and(common, phydev->lp_advertising, phydev->advertising);
+
+	for (i = 0; i < ARRAY_SIZE(settings); i++)
+		if (test_bit(settings[i].bit, common)) {
+			speed = settings[i].speed;
+			break;
+		}
+
+	if (speed == SPEED_UNKNOWN || phydev->speed >= speed)
+		return;
+
+	phydev_warn(phydev, "Downshift occurred from negotiated speed %s to actual speed %s, check cabling!\n",
+		    phy_speed_to_str(speed), phy_speed_to_str(phydev->speed));
+
+	phydev->downshifted_rate = 1;
+}
+EXPORT_SYMBOL_GPL(phy_check_downshift);
+
 static int phy_resolve_min_speed(struct phy_device *phydev, bool fdx_only)
 {
 	__ETHTOOL_DECLARE_LINK_MODE_MASK(common);

drivers/net/phy/phy.c

@@ -96,9 +96,10 @@ void phy_print_status(struct phy_device *phydev)
 {
 	if (phydev->link) {
 		netdev_info(phydev->attached_dev,
-			"Link is Up - %s/%s - flow control %s\n",
+			"Link is Up - %s/%s %s- flow control %s\n",
 			phy_speed_to_str(phydev->speed),
 			phy_duplex_to_str(phydev->duplex),
+			phydev->downshifted_rate ? "(downshifted) " : "",
 			phy_pause_str(phydev));
 	} else	{
 		netdev_info(phydev->attached_dev, "Link is Down\n");
@@ -507,6 +508,7 @@ static int phy_check_link_status(struct phy_device *phydev)
 		return err;
 
 	if (phydev->link && phydev->state != PHY_RUNNING) {
+		phy_check_downshift(phydev);
 		phydev->state = PHY_RUNNING;
 		phy_link_up(phydev);
 	} else if (!phydev->link && phydev->state != PHY_NOLINK) {

include/linux/phy.h

@@ -365,6 +365,7 @@ struct macsec_ops;
  * suspended_by_mdio_bus: Set to true if this phy was suspended by MDIO bus.
  * sysfs_links: Internal boolean tracking sysfs symbolic links setup/removal.
  * loopback_enabled: Set true if this phy has been loopbacked successfully.
+ * downshifted_rate: Set true if link speed has been downshifted.
  * state: state of the PHY for management purposes
  * dev_flags: Device-specific flags used by the PHY driver.
  * irq: IRQ number of the PHY's interrupt (-1 if none)
@@ -405,6 +406,7 @@ struct phy_device {
 	unsigned suspended_by_mdio_bus:1;
 	unsigned sysfs_links:1;
 	unsigned loopback_enabled:1;
+	unsigned downshifted_rate:1;
 
 	unsigned autoneg:1;
 	/* The most recently read link state */
@@ -698,6 +700,7 @@ static inline bool phy_is_started(struct phy_device *phydev)
 
 void phy_resolve_aneg_pause(struct phy_device *phydev);
 void phy_resolve_aneg_linkmode(struct phy_device *phydev);
+void phy_check_downshift(struct phy_device *phydev);
 
 /**
  * phy_read - Convenience function for reading a given PHY register