net: phy: dp83867: enable robust auto-mdix

The link detection timeouts can be observed (or link might not be detected
at all) when dp83867 PHY is configured in manual mode (speed/duplex).

CFG3[9] Robust Auto-MDIX option allows to significantly improve link detection
in case dp83867 is configured in manual mode and reduce link detection
time.
As per DM: "If link partners are configured to operational modes that are
not supported by normal Auto MDI/MDIX mode (like Auto-Neg versus Force
100Base-TX or Force 100Base-TX versus Force 100Base-TX), this Robust Auto
MDI/MDIX mode allows MDI/MDIX resolution and prevents deadlock."

Hence, enable this option by default as there are no known reasons
not to do so.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83867.c

@@ -95,6 +95,10 @@
 #define DP83867_IO_MUX_CFG_CLK_O_SEL_MASK	(0x1f << 8)
 #define DP83867_IO_MUX_CFG_CLK_O_SEL_SHIFT	8
 
+/* CFG3 bits */
+#define DP83867_CFG3_INT_OE			BIT(7)
+#define DP83867_CFG3_ROBUST_AUTO_MDIX		BIT(9)
+
 /* CFG4 bits */
 #define DP83867_CFG4_PORT_MIRROR_EN              BIT(0)
 
@@ -410,12 +414,13 @@ static int dp83867_config_init(struct phy_device *phydev)
 		phy_write_mmd(phydev, DP83867_DEVADDR, DP83867_SGMIICTL, val);
 	}
 
+	val = phy_read(phydev, DP83867_CFG3);
 	/* Enable Interrupt output INT_OE in CFG3 register */
-	if (phy_interrupt_is_valid(phydev)) {
-		val = phy_read(phydev, DP83867_CFG3);
-		val |= BIT(7);
-		phy_write(phydev, DP83867_CFG3, val);
-	}
+	if (phy_interrupt_is_valid(phydev))
+		val |= DP83867_CFG3_INT_OE;
+
+	val |= DP83867_CFG3_ROBUST_AUTO_MDIX;
+	phy_write(phydev, DP83867_CFG3, val);
 
 	if (dp83867->port_mirroring != DP83867_PORT_MIRROING_KEEP)
 		dp83867_config_port_mirroring(phydev);