net: phy: marvell: fix m88e1111_set_downshift

Changing downshift params without software reset has no effect,
so call genphy_soft_reset() after change downshift params.

As the datasheet says:
Changes to these bits are disruptive to the normal operation therefore,
any changes to these registers must be followed by software reset
to take effect.

Fixes: 5c6bc5199b ("net: phy: marvell: add downshift support for M88E1111")
Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/marvell.c

@@ -967,22 +967,28 @@ static int m88e1111_get_downshift(struct phy_device *phydev, u8 *data)
 
 static int m88e1111_set_downshift(struct phy_device *phydev, u8 cnt)
 {
-	int val;
+	int val, err;
 
 	if (cnt > MII_M1111_PHY_EXT_CR_DOWNSHIFT_MAX)
 		return -E2BIG;
 
-	if (!cnt)
-		return phy_clear_bits(phydev, MII_M1111_PHY_EXT_CR,
-				      MII_M1111_PHY_EXT_CR_DOWNSHIFT_EN);
+	if (!cnt) {
+		err = phy_clear_bits(phydev, MII_M1111_PHY_EXT_CR,
+				     MII_M1111_PHY_EXT_CR_DOWNSHIFT_EN);
+	} else {
+		val = MII_M1111_PHY_EXT_CR_DOWNSHIFT_EN;
+		val |= FIELD_PREP(MII_M1111_PHY_EXT_CR_DOWNSHIFT_MASK, cnt - 1);
 
-	val = MII_M1111_PHY_EXT_CR_DOWNSHIFT_EN;
-	val |= FIELD_PREP(MII_M1111_PHY_EXT_CR_DOWNSHIFT_MASK, cnt - 1);
+		err = phy_modify(phydev, MII_M1111_PHY_EXT_CR,
+				 MII_M1111_PHY_EXT_CR_DOWNSHIFT_EN |
+				 MII_M1111_PHY_EXT_CR_DOWNSHIFT_MASK,
+				 val);
+	}
 
-	return phy_modify(phydev, MII_M1111_PHY_EXT_CR,
-			  MII_M1111_PHY_EXT_CR_DOWNSHIFT_EN |
-			  MII_M1111_PHY_EXT_CR_DOWNSHIFT_MASK,
-			  val);
+	if (err < 0)
+		return err;
+
+	return genphy_soft_reset(phydev);
 }
 
 static int m88e1111_get_tunable(struct phy_device *phydev,