net: phy: add a Kconfig option for mdio_devres

If phylib is built as a module and CONFIG_MDIO_DEVICE is 'y', the
mdio_device and mdio_bus code will be in the phylib module, not in the
kernel image. Meanwhile we build mdio_devres depending on the
CONFIG_MDIO_DEVICE symbol, so if it's 'y', it will go into the kernel
and we'll hit the following linker error:

   ld: drivers/net/phy/mdio_devres.o: in function `devm_mdiobus_alloc_size':
>> drivers/net/phy/mdio_devres.c:38: undefined reference to `mdiobus_alloc_size'
   ld: drivers/net/phy/mdio_devres.o: in function `devm_mdiobus_free':
>> drivers/net/phy/mdio_devres.c:16: undefined reference to `mdiobus_free'
   ld: drivers/net/phy/mdio_devres.o: in function `__devm_mdiobus_register':
>> drivers/net/phy/mdio_devres.c:87: undefined reference to `__mdiobus_register'
   ld: drivers/net/phy/mdio_devres.o: in function `devm_mdiobus_unregister':
>> drivers/net/phy/mdio_devres.c:53: undefined reference to `mdiobus_unregister'
   ld: drivers/net/phy/mdio_devres.o: in function `devm_of_mdiobus_register':
>> drivers/net/phy/mdio_devres.c:120: undefined reference to `of_mdiobus_register'

Add a hidden Kconfig option for MDIO_DEVRES which will be currently
selected by CONFIG_PHYLIB as there are no non-phylib users of these
helpers.
Reported-by: kernel test robot <lkp@intel.com>
Fixes: ac3a68d5 ("net: phy: don't abuse devres in devm_mdiobus_register()")
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/Kconfig

@@ -21,6 +21,9 @@ config MDIO_BUS
 
 if MDIO_BUS
 
+config MDIO_DEVRES
+	tristate
+
 config MDIO_ASPEED
 	tristate "ASPEED MDIO bus controller"
 	depends on ARCH_ASPEED || COMPILE_TEST
@@ -252,6 +255,7 @@ menuconfig PHYLIB
 	tristate "PHY Device support and infrastructure"
 	depends on NETDEVICES
 	select MDIO_DEVICE
+	select MDIO_DEVRES
 	help
 	  Ethernet controllers are usually attached to PHY
 	  devices.  This option provides infrastructure for

drivers/net/phy/Makefile

@@ -4,7 +4,6 @@
 libphy-y			:= phy.o phy-c45.o phy-core.o phy_device.o \
 				   linkmode.o
 mdio-bus-y			+= mdio_bus.o mdio_device.o
-mdio-devres-y			+= mdio_devres.o
 
 ifdef CONFIG_MDIO_DEVICE
 obj-y				+= mdio-boardinfo.o
@@ -18,7 +17,7 @@ libphy-y			+= $(mdio-bus-y)
 else
 obj-$(CONFIG_MDIO_DEVICE)	+= mdio-bus.o
 endif
-obj-$(CONFIG_MDIO_DEVICE)	+= mdio-devres.o
+obj-$(CONFIG_MDIO_DEVRES)	+= mdio_devres.o
 libphy-$(CONFIG_SWPHY)		+= swphy.o
 libphy-$(CONFIG_LED_TRIGGER_PHY)	+= phy_led_triggers.o