net: phy: dp83867: Fix initialization of PHYCR register

When initializing the PHY control register, the FIFO depth bits are
written without reading the previous register value, i.e. all other
bits are overwritten with zero. This disables automatic MDI-X
configuration, which is enabled by default. Fix initialization by doing
a read/modify/write operation.
Signed-off-by: Stefan Hauser <stefan@shauser.net>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83867.c

@@ -57,6 +57,7 @@
 
 /* PHY CTRL bits */
 #define DP83867_PHYCR_FIFO_DEPTH_SHIFT		14
+#define DP83867_PHYCR_FIFO_DEPTH_MASK		(3 << 14)
 
 /* RGMIIDCTL bits */
 #define DP83867_RGMII_TX_CLK_DELAY_SHIFT	4
@@ -133,8 +134,8 @@ static int dp83867_of_init(struct phy_device *phydev)
 static int dp83867_config_init(struct phy_device *phydev)
 {
 	struct dp83867_private *dp83867;
-	int ret;
-	u16 val, delay;
+	int ret, val;
+	u16 delay;
 
 	if (!phydev->priv) {
 		dp83867 = devm_kzalloc(&phydev->mdio.dev, sizeof(*dp83867),
@@ -151,8 +152,12 @@ static int dp83867_config_init(struct phy_device *phydev)
 	}
 
 	if (phy_interface_is_rgmii(phydev)) {
-		ret = phy_write(phydev, MII_DP83867_PHYCTRL,
-			(dp83867->fifo_depth << DP83867_PHYCR_FIFO_DEPTH_SHIFT));
+		val = phy_read(phydev, MII_DP83867_PHYCTRL);
+		if (val < 0)
+			return val;
+		val &= ~DP83867_PHYCR_FIFO_DEPTH_MASK;
+		val |= (dp83867->fifo_depth << DP83867_PHYCR_FIFO_DEPTH_SHIFT);
+		ret = phy_write(phydev, MII_DP83867_PHYCTRL, val);
 		if (ret)
 			return ret;
 	}