net: mdio-mux: fix C45 access returning -EIO after API change

The mii_bus API conversion to read_c45() and write_c45() did not cover
the mdio-mux driver before read() and write() were made C22-only.

This broke arch/arm64/boot/dts/freescale/fsl-ls1028a-qds-13bb.dtso.
The -EOPNOTSUPP from mdiobus_c45_read() is transformed by
get_phy_c45_devs_in_pkg() into -EIO, is further propagated to
of_mdiobus_register() and this makes the mdio-mux driver fail to probe
the entire child buses, not just the PHYs that cause access errors.

Fix the regression by introducing special c45 read and write accessors
to mdio-mux which forward the operation to the parent MDIO bus.

Fixes: db1a63a ("net: phy: Remove fallback to old C45 method")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20231017143144.3212657-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: vladimiroltean

drivers/net/mdio/mdio-mux.c

@@ -55,6 +55,27 @@ static int mdio_mux_read(struct mii_bus *bus, int phy_id, int regnum)
 	return r;
 }
 
+static int mdio_mux_read_c45(struct mii_bus *bus, int phy_id, int dev_addr,
+			     int regnum)
+{
+	struct mdio_mux_child_bus *cb = bus->priv;
+	struct mdio_mux_parent_bus *pb = cb->parent;
+	int r;
+
+	mutex_lock_nested(&pb->mii_bus->mdio_lock, MDIO_MUTEX_MUX);
+	r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data);
+	if (r)
+		goto out;
+
+	pb->current_child = cb->bus_number;
+
+	r = pb->mii_bus->read_c45(pb->mii_bus, phy_id, dev_addr, regnum);
+out:
+	mutex_unlock(&pb->mii_bus->mdio_lock);
+
+	return r;
+}
+
 /*
  * The parent bus' lock is used to order access to the switch_fn.
  */
@@ -80,6 +101,28 @@ static int mdio_mux_write(struct mii_bus *bus, int phy_id,
 	return r;
 }
 
+static int mdio_mux_write_c45(struct mii_bus *bus, int phy_id, int dev_addr,
+			      int regnum, u16 val)
+{
+	struct mdio_mux_child_bus *cb = bus->priv;
+	struct mdio_mux_parent_bus *pb = cb->parent;
+
+	int r;
+
+	mutex_lock_nested(&pb->mii_bus->mdio_lock, MDIO_MUTEX_MUX);
+	r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data);
+	if (r)
+		goto out;
+
+	pb->current_child = cb->bus_number;
+
+	r = pb->mii_bus->write_c45(pb->mii_bus, phy_id, dev_addr, regnum, val);
+out:
+	mutex_unlock(&pb->mii_bus->mdio_lock);
+
+	return r;
+}
+
 static int parent_count;
 
 static void mdio_mux_uninit_children(struct mdio_mux_parent_bus *pb)
@@ -173,6 +216,10 @@ int mdio_mux_init(struct device *dev,
 		cb->mii_bus->parent = dev;
 		cb->mii_bus->read = mdio_mux_read;
 		cb->mii_bus->write = mdio_mux_write;
+		if (parent_bus->read_c45)
+			cb->mii_bus->read_c45 = mdio_mux_read_c45;
+		if (parent_bus->write_c45)
+			cb->mii_bus->write_c45 = mdio_mux_write_c45;
 		r = of_mdiobus_register(cb->mii_bus, child_bus_node);
 		if (r) {
 			mdiobus_free(cb->mii_bus);