net: dsa: mv88e6xxx: improve 88e6352 serdes statistics detection

The decision whether to report serdes statistics currently depends on
the cached C_Mode value for the port, read at probe time or updated by
configuration. However, port 4 can be in "automedia" mode when it is
used as a serdes port, meaning it switches between the internal PHY and
the serdes, changing the read-only C_Mode value depending on which
first gains link. Consequently, the C_Mode value read at probe does not
accurately reflect whether the port has the serdes associated with it.

In "net: dsa: mv88e6xxx: add mv88e6352_g2_scratch_port_has_serdes()",
we added a way to read the hardware configuration to determine which
port has the serdes associated with it. Use this to determine which
port reports the serdes statistics.
Reviewed-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/serdes.c

@@ -272,14 +272,6 @@ int mv88e6352_serdes_get_lane(struct mv88e6xxx_chip *chip, int port)
 	return lane;
 }
 
-static bool mv88e6352_port_has_serdes(struct mv88e6xxx_chip *chip, int port)
-{
-	if (mv88e6xxx_serdes_get_lane(chip, port) >= 0)
-		return true;
-
-	return false;
-}
-
 struct mv88e6352_serdes_hw_stat {
 	char string[ETH_GSTRING_LEN];
 	int sizeof_stat;
@@ -293,20 +285,24 @@ static struct mv88e6352_serdes_hw_stat mv88e6352_serdes_hw_stats[] = {
 
 int mv88e6352_serdes_get_sset_count(struct mv88e6xxx_chip *chip, int port)
 {
-	if (mv88e6352_port_has_serdes(chip, port))
-		return ARRAY_SIZE(mv88e6352_serdes_hw_stats);
+	int err;
 
-	return 0;
+	err = mv88e6352_g2_scratch_port_has_serdes(chip, port);
+	if (err <= 0)
+		return err;
+
+	return ARRAY_SIZE(mv88e6352_serdes_hw_stats);
 }
 
 int mv88e6352_serdes_get_strings(struct mv88e6xxx_chip *chip,
 				 int port, uint8_t *data)
 {
 	struct mv88e6352_serdes_hw_stat *stat;
-	int i;
+	int err, i;
 
-	if (!mv88e6352_port_has_serdes(chip, port))
-		return 0;
+	err = mv88e6352_g2_scratch_port_has_serdes(chip, port);
+	if (err <= 0)
+		return err;
 
 	for (i = 0; i < ARRAY_SIZE(mv88e6352_serdes_hw_stats); i++) {
 		stat = &mv88e6352_serdes_hw_stats[i];
@@ -348,11 +344,12 @@ int mv88e6352_serdes_get_stats(struct mv88e6xxx_chip *chip, int port,
 {
 	struct mv88e6xxx_port *mv88e6xxx_port = &chip->ports[port];
 	struct mv88e6352_serdes_hw_stat *stat;
+	int i, err;
 	u64 value;
-	int i;
 
-	if (!mv88e6352_port_has_serdes(chip, port))
-		return 0;
+	err = mv88e6352_g2_scratch_port_has_serdes(chip, port);
+	if (err <= 0)
+		return err;
 
 	BUILD_BUG_ON(ARRAY_SIZE(mv88e6352_serdes_hw_stats) >
 		     ARRAY_SIZE(mv88e6xxx_port->serdes_stats));
@@ -419,8 +416,13 @@ unsigned int mv88e6352_serdes_irq_mapping(struct mv88e6xxx_chip *chip, int port)
 
 int mv88e6352_serdes_get_regs_len(struct mv88e6xxx_chip *chip, int port)
 {
-	if (!mv88e6352_port_has_serdes(chip, port))
-		return 0;
+	int err;
+
+	mv88e6xxx_reg_lock(chip);
+	err = mv88e6352_g2_scratch_port_has_serdes(chip, port);
+	mv88e6xxx_reg_unlock(chip);
+	if (err <= 0)
+		return err;
 
 	return 32 * sizeof(u16);
 }
@@ -432,7 +434,8 @@ void mv88e6352_serdes_get_regs(struct mv88e6xxx_chip *chip, int port, void *_p)
 	int err;
 	int i;
 
-	if (!mv88e6352_port_has_serdes(chip, port))
+	err = mv88e6352_g2_scratch_port_has_serdes(chip, port);
+	if (err <= 0)
 		return;
 
 	for (i = 0 ; i < 32; i++) {