net: mii: add mii_bmcr_encode_fixed()

Add a function to encode a fixed speed/duplex to a BMCR value.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/mii.h

@@ -545,4 +545,39 @@ static inline u8 mii_resolve_flowctrl_fdx(u16 lcladv, u16 rmtadv)
 	return cap;
 }
 
+/**
+ * mii_bmcr_encode_fixed - encode fixed speed/duplex settings to a BMCR value
+ * @speed: a SPEED_* value
+ * @duplex: a DUPLEX_* value
+ *
+ * Encode the speed and duplex to a BMCR value. 2500, 1000, 100 and 10 Mbps are
+ * supported. 2500Mbps is encoded to 1000Mbps. Other speeds are encoded as 10
+ * Mbps. Unknown duplex values are encoded to half-duplex.
+ */
+static inline u16 mii_bmcr_encode_fixed(int speed, int duplex)
+{
+	u16 bmcr;
+
+	switch (speed) {
+	case SPEED_2500:
+	case SPEED_1000:
+		bmcr = BMCR_SPEED1000;
+		break;
+
+	case SPEED_100:
+		bmcr = BMCR_SPEED100;
+		break;
+
+	case SPEED_10:
+	default:
+		bmcr = BMCR_SPEED10;
+		break;
+	}
+
+	if (duplex == DUPLEX_FULL)
+		bmcr |= BMCR_FULLDPLX;
+
+	return bmcr;
+}
+
 #endif /* __LINUX_MII_H__ */