net: mdio: add helpers to extract clause 45 regad and devad fields

Add a couple of helpers and definitions to extract the clause 45 regad
and devad fields from the regnum passed into MDIO drivers.
Tested-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/mdio.h

@@ -7,6 +7,7 @@
 #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
@@ -14,6 +15,7 @@
  */
 #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;
@@ -381,6 +383,16 @@ 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)
 {