net: phy: marvell: add sleep time after enabling the loopback bit

Sleep time is added to ensure the phy to be ready after loopback
bit was set. This to prevent the phy loopback test from failing.

Fixes: 020a45af ("net: phy: marvell: add Marvell specific PHY loopback")
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Signed-off-by: Aminuddin Jamaluddin <aminuddin.jamaluddin@intel.com>
Link: https://lore.kernel.org/r/20221114065302.10625-1-aminuddin.jamaluddin@intel.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/phy/marvell.c

@@ -2015,14 +2015,16 @@ static int m88e1510_loopback(struct phy_device *phydev, bool enable)
 		if (err < 0)
 			return err;
 
-		/* FIXME: Based on trial and error test, it seem 1G need to have
-		 * delay between soft reset and loopback enablement.
-		 */
-		if (phydev->speed == SPEED_1000)
-			msleep(1000);
+		err = phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
+				 BMCR_LOOPBACK);
 
-		return phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
-				  BMCR_LOOPBACK);
+		if (!err) {
+			/* It takes some time for PHY device to switch
+			 * into/out-of loopback mode.
+			 */
+			msleep(1000);
+		}
+		return err;
 	} else {
 		err = phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK, 0);
 		if (err < 0)