net: phy: workaround for buggy cable detection by LAN8700 after cable plugging

* Due to HW bug, LAN8700 sometimes does not detect presence of energy in the
  Ethernet cable in Energy Detect Power-Down mode (e.g while EDPWRDOWN bit is
  set, the ENERGYON bit does not asserted sometimes). This is a common bug of
  LAN87xx family of PHY chips.
* The lan87xx_read_status() was improved to acquire ENERGYON bit. Its previous
  algorythm still not reliable on 100 % and sometimes skip cable plugging.

Signed-off-by: Igor Plyatov <plyatov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/smsc.c

@@ -91,19 +91,18 @@ static int lan911x_config_init(struct phy_device *phydev)
 }
 
 /*
- * The LAN8710/LAN8720 requires a minimum of 2 link pulses within 64ms of each
- * other in order to set the ENERGYON bit and exit EDPD mode.  If a link partner
- * does send the pulses within this interval, the PHY will remained powered
- * down.
- *
- * This workaround will manually toggle the PHY on/off upon calls to read_status
- * in order to generate link test pulses if the link is down.  If a link partner
- * is present, it will respond to the pulses, which will cause the ENERGYON bit
- * to be set and will cause the EDPD mode to be exited.
+ * The LAN87xx suffers from rare absence of the ENERGYON-bit when Ethernet cable
+ * plugs in while LAN87xx is in Energy Detect Power-Down mode. This leads to
+ * unstable detection of plugging in Ethernet cable.
+ * This workaround disables Energy Detect Power-Down mode and waiting for
+ * response on link pulses to detect presence of plugged Ethernet cable.
+ * The Energy Detect Power-Down mode is enabled again in the end of procedure to
+ * save approximately 220 mW of power if cable is unplugged.
  */
 static int lan87xx_read_status(struct phy_device *phydev)
 {
 	int err = genphy_read_status(phydev);
+	int i;
 
 	if (!phydev->link) {
 		/* Disable EDPD to wake up PHY */
@@ -116,8 +115,16 @@ static int lan87xx_read_status(struct phy_device *phydev)
 		if (rc < 0)
 			return rc;
 
-		/* Sleep 64 ms to allow ~5 link test pulses to be sent */
-		msleep(64);
+		/* Wait max 640 ms to detect energy */
+		for (i = 0; i < 64; i++) {
+			/* Sleep to allow link test pulses to be sent */
+			msleep(10);
+			rc = phy_read(phydev, MII_LAN83C185_CTRL_STATUS);
+			if (rc < 0)
+				return rc;
+			if (rc & MII_LAN83C185_ENERGYON)
+				break;
+		};
 
 		/* Re-enable EDPD */
 		rc = phy_read(phydev, MII_LAN83C185_CTRL_STATUS);
@@ -191,7 +198,7 @@ static struct phy_driver smsc_phy_driver[] = {
 
 	/* basic functions */
 	.config_aneg	= genphy_config_aneg,
-	.read_status	= genphy_read_status,
+	.read_status	= lan87xx_read_status,
 	.config_init	= smsc_phy_config_init,
 	.soft_reset	= smsc_phy_reset,