net: phy: mxl-gpy: enhance delay time required by loopback disable function

GPY2xx devices need 3 seconds to fully switch out of loopback mode
before it can safely re-enter loopback mode. Implement timeout mechanism
to guarantee 3 seconds waited before re-enter loopback mode.
Signed-off-by: Xu Liang <lxu@maxlinear.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mxl-gpy.c

@@ -107,6 +107,13 @@ struct gpy_priv {
 
 	u8 fw_major;
 	u8 fw_minor;
+
+	/* It takes 3 seconds to fully switch out of loopback mode before
+	 * it can safely re-enter loopback mode. Record the time when
+	 * loopback is disabled. Check and wait if necessary before loopback
+	 * is enabled.
+	 */
+	u64 lb_dis_to;
 };
 
 static const struct {
@@ -769,18 +776,34 @@ static void gpy_get_wol(struct phy_device *phydev,
 
 static int gpy_loopback(struct phy_device *phydev, bool enable)
 {
+	struct gpy_priv *priv = phydev->priv;
+	u16 set = 0;
 	int ret;
 
-	ret = phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
-			 enable ? BMCR_LOOPBACK : 0);
-	if (!ret) {
-		/* It takes some time for PHY device to switch
-		 * into/out-of loopback mode.
+	if (enable) {
+		u64 now = get_jiffies_64();
+
+		/* wait until 3 seconds from last disable */
+		if (time_before64(now, priv->lb_dis_to))
+			msleep(jiffies64_to_msecs(priv->lb_dis_to - now));
+
+		set = BMCR_LOOPBACK;
+	}
+
+	ret = phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK, set);
+	if (ret <= 0)
+		return ret;
+
+	if (enable) {
+		/* It takes some time for PHY device to switch into
+		 * loopback mode.
 		 */
 		msleep(100);
+	} else {
+		priv->lb_dis_to = get_jiffies_64() + HZ * 3;
 	}
 
-	return ret;
+	return 0;
 }
 
 static int gpy115_loopback(struct phy_device *phydev, bool enable)