net: mdio: add mdiobus_modify_changed()

Add mdiobus_modify_changed() helper to reflect the phylib and similar
equivalents. This will avoid this functionality being open-coded, as
has already happened in phylink, and it looks like other users will be
appearing soon.
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/mdio_bus.c

@@ -926,6 +926,28 @@ int mdiobus_modify(struct mii_bus *bus, int addr, u32 regnum, u16 mask, u16 set)
 }
 EXPORT_SYMBOL_GPL(mdiobus_modify);
 
+/**
+ * mdiobus_modify_changed - Convenience function for modifying a given mdio
+ *	device register and returning if it changed
+ * @bus: the mii_bus struct
+ * @addr: the phy address
+ * @regnum: register number to write
+ * @mask: bit mask of bits to clear
+ * @set: bit mask of bits to set
+ */
+int mdiobus_modify_changed(struct mii_bus *bus, int addr, u32 regnum,
+			   u16 mask, u16 set)
+{
+	int err;
+
+	mutex_lock(&bus->mdio_lock);
+	err = __mdiobus_modify_changed(bus, addr, regnum, mask, set);
+	mutex_unlock(&bus->mdio_lock);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(mdiobus_modify_changed);
+
 /**
  * mdio_bus_match - determine if given MDIO driver supports the given
  *		    MDIO device

include/linux/mdio.h

@@ -349,6 +349,8 @@ 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);
 int mdiobus_modify(struct mii_bus *bus, int addr, u32 regnum, u16 mask,
 		   u16 set);
+int mdiobus_modify_changed(struct mii_bus *bus, int addr, u32 regnum,
+			   u16 mask, u16 set);
 
 static inline u32 mdiobus_c45_addr(int devad, u16 regnum)
 {