net: phy: Allow splitting MDIO bus/device support from PHYs

Introduce a new configuration symbol: MDIO_DEVICE which allows building
the MDIO devices and bus code, without pulling in the entire Ethernet
PHY library and devices code.

PHYLIB nows select MDIO_DEVICE and the relevant Makefile files are
updated to reflect that.

When MDIO_DEVICE (MDIO bus/device only) is selected, but not PHYLIB, we
have mdio-bus.ko as a loadable module, and it does not have a
module_exit() function because the safety of removing a bus class is
unclear.

When both MDIO_DEVICE and PHYLIB are enabled, we need to assemble
everything into a common loadable module: libphy.ko because of nasty
circular dependencies between phy.c, phy_device.c and mdio_bus.c which
are really tough to untangle.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 2efca6b..624cecf 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -745,8 +745,24 @@ int phy_write_mmd(struct phy_device *phydev, int devad, u32 regnum, u16 val);
 struct phy_device *phy_device_create(struct mii_bus *bus, int addr, int phy_id,
 				     bool is_c45,
 				     struct phy_c45_device_ids *c45_ids);
+#if IS_ENABLED(CONFIG_PHYLIB)
 struct phy_device *get_phy_device(struct mii_bus *bus, int addr, bool is_c45);
 int phy_device_register(struct phy_device *phy);
+void phy_device_free(struct phy_device *phydev);
+#else
+static inline
+struct phy_device *get_phy_device(struct mii_bus *bus, int addr, bool is_c45)
+{
+	return NULL;
+}
+
+static inline int phy_device_register(struct phy_device *phy)
+{
+	return 0;
+}
+
+static inline void phy_device_free(struct phy_device *phydev) { }
+#endif /* CONFIG_PHYLIB */
 void phy_device_remove(struct phy_device *phydev);
 int phy_init_hw(struct phy_device *phydev);
 int phy_suspend(struct phy_device *phydev);
@@ -827,7 +843,6 @@ int phy_ethtool_ksettings_set(struct phy_device *phydev,
 int phy_mii_ioctl(struct phy_device *phydev, struct ifreq *ifr, int cmd);
 int phy_start_interrupts(struct phy_device *phydev);
 void phy_print_status(struct phy_device *phydev);
-void phy_device_free(struct phy_device *phydev);
 int phy_set_max_speed(struct phy_device *phydev, u32 max_speed);
 
 int phy_register_fixup(const char *bus_id, u32 phy_uid, u32 phy_uid_mask,
@@ -854,8 +869,10 @@ int phy_ethtool_set_link_ksettings(struct net_device *ndev,
 				   const struct ethtool_link_ksettings *cmd);
 int phy_ethtool_nway_reset(struct net_device *ndev);
 
+#if IS_ENABLED(CONFIG_PHYLIB)
 int __init mdio_bus_init(void);
 void mdio_bus_exit(void);
+#endif
 
 extern struct bus_type mdio_bus_type;
 
@@ -866,7 +883,7 @@ struct mdio_board_info {
 	const void	*platform_data;
 };
 
-#if IS_ENABLED(CONFIG_PHYLIB)
+#if IS_ENABLED(CONFIG_MDIO_DEVICE)
 int mdiobus_register_board_info(const struct mdio_board_info *info,
 				unsigned int n);
 #else