net: dsa: mv88e6xxx: implement port_set_speed for mv88e6250

The data sheet also mentions the possibility of selecting 200 Mbps for
the MII ports (ports 5 and 6) by setting the ForceSpd field to
0x2 (aka MV88E6065_PORT_MAC_CTL_SPEED_200). However, there's a note
that "actual speed is determined by bit 8 above", and flipping back a
page, one finds that bits 13:8 are reserved...

So without further information on what bit 8 means, let's stick to
supporting just 10 and 100 Mbps on all ports.
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NRasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/port.c

@@ -294,6 +294,18 @@ int mv88e6185_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed)
 	return mv88e6xxx_port_set_speed(chip, port, speed, false, false);
 }
 
+/* Support 10, 100 Mbps (e.g. 88E6250 family) */
+int mv88e6250_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed)
+{
+	if (speed == SPEED_MAX)
+		speed = 100;
+
+	if (speed > 100)
+		return -EOPNOTSUPP;
+
+	return mv88e6xxx_port_set_speed(chip, port, speed, false, false);
+}
+
 /* Support 10, 100, 200, 1000, 2500 Mbps (e.g. 88E6341) */
 int mv88e6341_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed)
 {

drivers/net/dsa/mv88e6xxx/port.h

@@ -279,6 +279,7 @@ int mv88e6xxx_port_set_duplex(struct mv88e6xxx_chip *chip, int port, int dup);
 
 int mv88e6065_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed);
 int mv88e6185_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed);
+int mv88e6250_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed);
 int mv88e6341_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed);
 int mv88e6352_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed);
 int mv88e6390_port_set_speed(struct mv88e6xxx_chip *chip, int port, int speed);