Re: [PATCH net-next v3 3/3] net: phy: Allow splitting MDIO bus/device support from PHYs

On Thu, Mar 23, 2017 at 6:01 PM, Florian Fainelli [off-list ref] wrote:

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.

I'm getting a couple of link errors with this:

- ARCH_ORION5X calls mdiobus_register_board_info and must force
  mdio-boardinfo.o to be built-in, but I don't see how it should
ideally do that:

arch/arm/plat-orion/common.o: In function `orion_ge00_switch_init':
common.c:(.init.text+0x6a6): undefined reference to
`mdiobus_register_board_info'

- sun4i_mdio.ko depends on mdiobus, but it gets selected from another driver
  which makes it built-in without checking if mdiobus is a module

drivers/net/built-in.o: In function `sun4i_mdio_remove':
:(.text+0x51c): undefined reference to `mdiobus_unregister'
:(.text+0x524): undefined reference to `mdiobus_free'
drivers/net/built-in.o: In function `sun4i_mdio_probe':
:(.text+0x728): undefined reference to `mdiobus_alloc_size'
:(.text+0x85c): undefined reference to `of_mdiobus_register'
:(.text+0x894): undefined reference to `mdiobus_free'

- Some drivers select MDIO_BITBANG, which may need to be a module:
warning: (FS_ENET_MDIO_FCC && AX88796 && SH_ETH && RAVB) selects
MDIO_BITBANG which has unmet direct dependencies (NETDEVICES &&
MDIO_DEVICE && (MDIO_DEVICE!=y || PHYLIB!=m))

I've been able to work around the latter two using this hack:

diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index 60ffc9da6a28..d82857f46cec 100644
--- a/drivers/net/phy/Kconfig
+++ b/drivers/net/phy/Kconfig

@@ -28,7 +28,7 @@ config MDIO_BCM_UNIMAC

 config MDIO_BITBANG
  tristate "Bitbanged MDIO buses"
- depends on !(MDIO_DEVICE=y && PHYLIB=m)
+ depends on m || !(MDIO_DEVICE=y && PHYLIB=m)
  help
   This module implements the MDIO bus protocol in software,
   for use by low level drivers that export the ability to

@@ -118,6 +118,7 @@ config MDIO_OCTEON
 config MDIO_SUN4I
  tristate "Allwinner sun4i MDIO interface support"
  depends on ARCH_SUNXI
+ depends on m || !(MDIO_DEVICE=y && PHYLIB=m)
  help
   This driver supports the MDIO interface found in the network
   interface units of the Allwinner SoC that have an EMAC (A10,


      Arnd