net: phy: factor out provider part from mdio_bus.c

After 52358dd ("net: phy: remove function stubs") there's a
problem if CONFIG_MDIO_BUS is set, but CONFIG_PHYLIB is not.
mdiobus_scan() uses phylib functions like get_phy_device().
Bringing back the stub wouldn't make much sense, because it would
allow to compile mdiobus_scan(), but the function would be unusable.
The stub returned NULL, and we have the following in mdiobus_scan():

phydev = get_phy_device(bus, addr, c45);
        if (IS_ERR(phydev))
                return phydev;

So calling mdiobus_scan() w/o CONFIG_PHYLIB would cause a crash later in
mdiobus_scan(). In general the PHYLIB functionality isn't optional here.
Consequently, MDIO bus providers depend on PHYLIB.
Therefore factor it out and build it together with the libphy core
modules. In addition make all MDIO bus providers under /drivers/net/mdio
depend on PHYLIB. Same applies to enetc MDIO bus provider. Note that
PHYLIB selects MDIO_DEVRES, therefore we can omit this here.

Fixes: 52358dd ("net: phy: remove function stubs")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Reviewed-by: Jacob Keller <[email protected]>
Signed-off-by: Heiner Kallweit <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: hkallweit

drivers/net/ethernet/freescale/enetc/Kconfig

@@ -73,8 +73,7 @@ config FSL_ENETC_IERB
 
 config FSL_ENETC_MDIO
 	tristate "ENETC MDIO driver"
-	depends on PCI && MDIO_BUS
-	select MDIO_DEVRES
+	depends on PCI && PHYLIB
 	help
 	  This driver supports NXP ENETC Central MDIO controller as a PCIe
 	  physical function (PF) device.

drivers/net/mdio/Kconfig

@@ -19,30 +19,25 @@ config MDIO_BUS
 	  reflects whether the mdio_bus/mdio_device code is built as a
 	  loadable module or built-in.
 
+if PHYLIB
+
 config FWNODE_MDIO
-	def_tristate PHYLIB
-	depends on (ACPI || OF) || COMPILE_TEST
+	def_tristate (ACPI || OF) || COMPILE_TEST
 	select FIXED_PHY
 	help
 	  FWNODE MDIO bus (Ethernet PHY) accessors
 
 config OF_MDIO
-	def_tristate PHYLIB
-	depends on OF
-	depends on PHYLIB
+	def_tristate OF
 	select FIXED_PHY
 	help
 	  OpenFirmware MDIO bus (Ethernet PHY) accessors
 
 config ACPI_MDIO
-	def_tristate PHYLIB
-	depends on ACPI
-	depends on PHYLIB
+	def_tristate ACPI
 	help
 	  ACPI MDIO bus (Ethernet PHY) accessors
 
-if MDIO_BUS
-
 config MDIO_DEVRES
 	tristate
 
@@ -57,7 +52,6 @@ config MDIO_SUN4I
 config MDIO_XGENE
 	tristate "APM X-Gene SoC MDIO bus controller"
 	depends on ARCH_XGENE || COMPILE_TEST
-	depends on PHYLIB
 	help
 	  This module provides a driver for the MDIO busses found in the
 	  APM X-Gene SoC's.

drivers/net/phy/Makefile

@@ -3,7 +3,7 @@
 
 libphy-y			:= phy.o phy-c45.o phy-core.o phy_device.o \
 				   linkmode.o phy_link_topology.o \
-				   phy_package.o phy_caps.o
+				   phy_package.o phy_caps.o mdio_bus_provider.o
 mdio-bus-y			+= mdio_bus.o mdio_device.o
 
 ifdef CONFIG_MDIO_DEVICE