[net-next] net: pcs-xpcs: depend on MDIO_BUS instead of selecting it

The below compile time error can be seen when PHYLIB is configured as a
module.

 ld: drivers/net/pcs/pcs-xpcs.o: in function `xpcs_read':
 pcs-xpcs.c:(.text+0x29): undefined reference to `mdiobus_read'
 ld: drivers/net/pcs/pcs-xpcs.o: in function `xpcs_soft_reset.constprop.7':
 pcs-xpcs.c:(.text+0x80): undefined reference to `mdiobus_write'
 ld: drivers/net/pcs/pcs-xpcs.o: in function `xpcs_config_aneg':
 pcs-xpcs.c:(.text+0x318): undefined reference to `mdiobus_write'
 ld: pcs-xpcs.c:(.text+0x38e): undefined reference to `mdiobus_write'
 ld: pcs-xpcs.c:(.text+0x3eb): undefined reference to `mdiobus_write'
 ld: pcs-xpcs.c:(.text+0x437): undefined reference to `mdiobus_write'
 ld: drivers/net/pcs/pcs-xpcs.o:pcs-xpcs.c:(.text+0xb1e): more undefined references to `mdiobus_write' follow

PHYLIB being a module leads to MDIO_BUS being a module as well while the
XPCS is still built-in. What should happen in this configuration is that
PCS_XPCS should be forced to build as module. However, that select only
acts in the opposite way so we should turn it into a depends.

Fix this up by explicitly depending on MDIO_BUS.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Fixes: 2fa4e4b799e1 ("net: pcs: Move XPCS into new PCS subdirectory")
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
---
 drivers/net/pcs/Kconfig | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

On Thu, 15 Oct 2020 23:00:23 +0300 Ioana Ciornei wrote:
> The below compile time error can be seen when PHYLIB is configured as a
> module.
> 
>  ld: drivers/net/pcs/pcs-xpcs.o: in function `xpcs_read':
>  pcs-xpcs.c:(.text+0x29): undefined reference to `mdiobus_read'
>  ld: drivers/net/pcs/pcs-xpcs.o: in function `xpcs_soft_reset.constprop.7':
>  pcs-xpcs.c:(.text+0x80): undefined reference to `mdiobus_write'
>  ld: drivers/net/pcs/pcs-xpcs.o: in function `xpcs_config_aneg':
>  pcs-xpcs.c:(.text+0x318): undefined reference to `mdiobus_write'
>  ld: pcs-xpcs.c:(.text+0x38e): undefined reference to `mdiobus_write'
>  ld: pcs-xpcs.c:(.text+0x3eb): undefined reference to `mdiobus_write'
>  ld: pcs-xpcs.c:(.text+0x437): undefined reference to `mdiobus_write'
>  ld: drivers/net/pcs/pcs-xpcs.o:pcs-xpcs.c:(.text+0xb1e): more undefined references to `mdiobus_write' follow
> 
> PHYLIB being a module leads to MDIO_BUS being a module as well while the
> XPCS is still built-in. What should happen in this configuration is that
> PCS_XPCS should be forced to build as module. However, that select only
> acts in the opposite way so we should turn it into a depends.
> 
> Fix this up by explicitly depending on MDIO_BUS.
> 
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
> Fixes: 2fa4e4b799e1 ("net: pcs: Move XPCS into new PCS subdirectory")
> Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>

Applied, thanks!