net: dsa: mv88e6xxx: kill last locked reg_read

Get rid of the last usage of the locked mv88e6xxx_reg_read function with
a new mv88e6xxx_port_read helper, useful later for chips with different
port registers base address.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -254,17 +254,6 @@ static int _mv88e6xxx_reg_read(struct mv88e6xxx_chip *chip, int addr, int reg)
 	return val;
 }
 
-static int mv88e6xxx_reg_read(struct mv88e6xxx_chip *chip, int addr, int reg)
-{
-	int ret;
-
-	mutex_lock(&chip->reg_lock);
-	ret = _mv88e6xxx_reg_read(chip, addr, reg);
-	mutex_unlock(&chip->reg_lock);
-
-	return ret;
-}
-
 static int _mv88e6xxx_reg_write(struct mv88e6xxx_chip *chip, int addr,
 				int reg, u16 val)
 {
@@ -2426,6 +2415,17 @@ static int mv88e6xxx_power_on_serdes(struct mv88e6xxx_chip *chip)
 	return ret;
 }
 
+static int mv88e6xxx_port_read(struct mv88e6xxx_chip *chip, int port,
+			       int reg, u16 *val)
+{
+	int addr = chip->info->port_base_addr + port;
+
+	if (port >= chip->info->num_ports)
+		return -EINVAL;
+
+	return mv88e6xxx_read(chip, addr, reg, val);
+}
+
 static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 {
 	struct dsa_switch *ds = chip->ds;
@@ -3830,12 +3830,15 @@ static const struct mv88e6xxx_info *mv88e6xxx_lookup_info(unsigned int prod_num)
 static int mv88e6xxx_detect(struct mv88e6xxx_chip *chip)
 {
 	const struct mv88e6xxx_info *info;
-	int id, prod_num, rev;
+	unsigned int prod_num, rev;
+	u16 id;
+	int err;
 
-	id = mv88e6xxx_reg_read(chip, chip->info->port_base_addr,
-				PORT_SWITCH_ID);
-	if (id < 0)
-		return id;
+	mutex_lock(&chip->reg_lock);
+	err = mv88e6xxx_port_read(chip, 0, PORT_SWITCH_ID, &id);
+	mutex_unlock(&chip->reg_lock);
+	if (err)
+		return err;
 
 	prod_num = (id & 0xfff0) >> 4;
 	rev = id & 0x000f;