diff --git a/include/linux/mdio.h b/include/linux/mdio.h
index 0f1f784de..006d1c1e9 100644
--- a/include/linux/mdio.h
+++ b/include/linux/mdio.h
@@ -7,8 +7,17 @@
 #define __LINUX_MDIO_H__
 
 #include <uapi/linux/mdio.h>
+#include <linux/bitfield.h>
 #include <linux/mod_devicetable.h>
 
+/* Or MII_ADDR_C45 into regnum for read/write on mii_bus to enable the 21 bit
+ * IEEE 802.3ae clause 45 addressing mode used by 10GIGE phy chips.
+ */
+#define MII_ADDR_C45		(1<<30)
+#define MII_DEVADDR_C45_SHIFT	16
+#define MII_DEVADDR_C45_MASK	GENMASK(20, 16)
+#define MII_REGADDR_C45_MASK	GENMASK(15, 0)
+
 struct gpio_desc;
 struct mii_bus;
 
@@ -325,6 +334,46 @@ int mdiobus_read_nested(struct mii_bus *bus, int addr, u32 regnum);
 int mdiobus_write(struct mii_bus *bus, int addr, u32 regnum, u16 val);
 int mdiobus_write_nested(struct mii_bus *bus, int addr, u32 regnum, u16 val);
 
+static inline u32 mdiobus_c45_addr(int devad, u16 regnum)
+{
+	return MII_ADDR_C45 | devad << MII_DEVADDR_C45_SHIFT | regnum;
+}
+
+static inline u16 mdiobus_c45_regad(u32 regnum)
+{
+	return FIELD_GET(MII_REGADDR_C45_MASK, regnum);
+}
+
+static inline u16 mdiobus_c45_devad(u32 regnum)
+{
+	return FIELD_GET(MII_DEVADDR_C45_MASK, regnum);
+}
+
+static inline int __mdiobus_c45_read(struct mii_bus *bus, int prtad, int devad,
+				     u16 regnum)
+{
+	return __mdiobus_read(bus, prtad, mdiobus_c45_addr(devad, regnum));
+}
+
+static inline int __mdiobus_c45_write(struct mii_bus *bus, int prtad, int devad,
+				      u16 regnum, u16 val)
+{
+	return __mdiobus_write(bus, prtad, mdiobus_c45_addr(devad, regnum),
+			       val);
+}
+
+static inline int mdiobus_c45_read(struct mii_bus *bus, int prtad, int devad,
+				   u16 regnum)
+{
+	return mdiobus_read(bus, prtad, mdiobus_c45_addr(devad, regnum));
+}
+
+static inline int mdiobus_c45_write(struct mii_bus *bus, int prtad, int devad,
+				    u16 regnum, u16 val)
+{
+	return mdiobus_write(bus, prtad, mdiobus_c45_addr(devad, regnum), val);
+}
+
 int mdiobus_register_device(struct mdio_device *mdiodev);
 int mdiobus_unregister_device(struct mdio_device *mdiodev);
 bool mdiobus_is_registered_device(struct mii_bus *bus, int addr);
-- 
2.18.0