[PATCH net v3] net: phy: marvell: add sleep time after enabling the loopback bit

[Aminuddin Jamaluddin <aminuddin.jamaluddin@intel.com>]

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: 020a45aff119 ("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>

---
V2 -> V3: Fix review comments from Jakub
V1: https://patchwork.kernel.org/project/netdevbpf/patch/20220825082238.11056-1-aminuddin.jamaluddin@intel.com/
---
---
 drivers/net/phy/marvell.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/net/phy/marvell.c b/drivers/net/phy/marvell.c
index a3e810705ce2..860610ba4d00 100644
--- a/drivers/net/phy/marvell.c
+++ b/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)
-- 
2.17.1