net: dsa: qca8k: fix kernel panic with legacy mdio mapping

When the mdio legacy mapping is used the mii_bus priv registered by DSA
refer to the dsa switch struct instead of the qca8k_priv struct and
causes a kernel panic. Create dedicated function when the internal
dedicated mdio driver is used to properly handle the 2 different
implementation.

Fixes: 759bafb ("net: dsa: qca8k: add support for internal phy and internal mdio")
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/qca8k.c

@@ -643,10 +643,8 @@ qca8k_mdio_busy_wait(struct mii_bus *bus, u32 reg, u32 mask)
 }
 
 static int
-qca8k_mdio_write(struct mii_bus *salve_bus, int phy, int regnum, u16 data)
+qca8k_mdio_write(struct mii_bus *bus, int phy, int regnum, u16 data)
 {
-	struct qca8k_priv *priv = salve_bus->priv;
-	struct mii_bus *bus = priv->bus;
 	u16 r1, r2, page;
 	u32 val;
 	int ret;
@@ -682,10 +680,8 @@ qca8k_mdio_write(struct mii_bus *salve_bus, int phy, int regnum, u16 data)
 }
 
 static int
-qca8k_mdio_read(struct mii_bus *salve_bus, int phy, int regnum)
+qca8k_mdio_read(struct mii_bus *bus, int phy, int regnum)
 {
-	struct qca8k_priv *priv = salve_bus->priv;
-	struct mii_bus *bus = priv->bus;
 	u16 r1, r2, page;
 	u32 val;
 	int ret;
@@ -726,6 +722,24 @@ qca8k_mdio_read(struct mii_bus *salve_bus, int phy, int regnum)
 	return ret;
 }
 
+static int
+qca8k_internal_mdio_write(struct mii_bus *slave_bus, int phy, int regnum, u16 data)
+{
+	struct qca8k_priv *priv = slave_bus->priv;
+	struct mii_bus *bus = priv->bus;
+
+	return qca8k_mdio_write(bus, phy, regnum, data);
+}
+
+static int
+qca8k_internal_mdio_read(struct mii_bus *slave_bus, int phy, int regnum)
+{
+	struct qca8k_priv *priv = slave_bus->priv;
+	struct mii_bus *bus = priv->bus;
+
+	return qca8k_mdio_read(bus, phy, regnum);
+}
+
 static int
 qca8k_phy_write(struct dsa_switch *ds, int port, int regnum, u16 data)
 {
@@ -775,8 +789,8 @@ qca8k_mdio_register(struct qca8k_priv *priv, struct device_node *mdio)
 
 	bus->priv = (void *)priv;
 	bus->name = "qca8k slave mii";
-	bus->read = qca8k_mdio_read;
-	bus->write = qca8k_mdio_write;
+	bus->read = qca8k_internal_mdio_read;
+	bus->write = qca8k_internal_mdio_write;
 	snprintf(bus->id, MII_BUS_ID_SIZE, "qca8k-%d",
 		 ds->index);