of_mdio: select fixed phy support unconditionally

Calling the fixed-phy functions when CONFIG_FIXED_PHY=m as a previous
change tried cannot work if the caller is in built-in code:

drivers/of/built-in.o: In function `of_phy_register_fixed_link':
of_reserved_mem.c:(.text+0x85e0): undefined reference to `fixed_phy_register'

Making of_mdio depend on 'FIXED_PHY || !FIXED_PHY' would solve this
dependency by enforcing that OF_MDIO itself becomes a loadable module
when FIXED_PHY=y, but that creates a different dependency as it
breaks any built-in ethernet driver that uses of_mdio.

Making FIXED_PHY a bool option also cannot work, since it depends on
PHYLIB, which again is tristate.

This version now uses 'select FIXED_PHY' to ensure that the fixed-phy
portion of of_mdio is not optional. The main downside of this is
a small increase in code size for cases that do not need fixed phy
support, but it should avoid all of the link-time problems.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: d1bd330a22 ("of_mdio: Enable fixed PHY support if driver is a module")
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/of/Kconfig

@@ -74,6 +74,7 @@ config OF_NET
 config OF_MDIO
 	def_tristate PHYLIB
 	depends on PHYLIB
+	select FIXED_PHY
 	help
 	  OpenFirmware MDIO bus (Ethernet PHY) accessors
 

drivers/of/of_mdio.c

@@ -361,7 +361,6 @@ struct phy_device *of_phy_attach(struct net_device *dev,
 }
 EXPORT_SYMBOL(of_phy_attach);
 
-#if IS_ENABLED(CONFIG_FIXED_PHY)
 /*
  * of_phy_is_fixed_link() and of_phy_register_fixed_link() must
  * support two DT bindings:
@@ -451,4 +450,3 @@ int of_phy_register_fixed_link(struct device_node *np)
 	return -ENODEV;
 }
 EXPORT_SYMBOL(of_phy_register_fixed_link);
-#endif

include/linux/of_mdio.h

@@ -25,6 +25,8 @@ struct phy_device *of_phy_attach(struct net_device *dev,
 
 extern struct mii_bus *of_mdio_find_bus(struct device_node *mdio_np);
 extern int of_mdio_parse_addr(struct device *dev, const struct device_node *np);
+extern int of_phy_register_fixed_link(struct device_node *np);
+extern bool of_phy_is_fixed_link(struct device_node *np);
 
 #else /* CONFIG_OF */
 static inline int of_mdiobus_register(struct mii_bus *mdio, struct device_node *np)
@@ -67,12 +69,6 @@ static inline int of_mdio_parse_addr(struct device *dev,
 {
 	return -ENOSYS;
 }
-#endif /* CONFIG_OF */
-
-#if defined(CONFIG_OF) && IS_ENABLED(CONFIG_FIXED_PHY)
-extern int of_phy_register_fixed_link(struct device_node *np);
-extern bool of_phy_is_fixed_link(struct device_node *np);
-#else
 static inline int of_phy_register_fixed_link(struct device_node *np)
 {
 	return -ENOSYS;