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net: dsa: realtek: fix Kconfig to assure consistent driver linkage 

The kernel test robot reported a build failure:

or1k-linux-ld: drivers/net/dsa/realtek/realtek-smi.o:(.rodata+0x16c): undefined reference to `rtl8366rb_variant'

... with the following build configuration:

CONFIG_NET_DSA_REALTEK=y
CONFIG_NET_DSA_REALTEK_SMI=y
CONFIG_NET_DSA_REALTEK_RTL8365MB=y
CONFIG_NET_DSA_REALTEK_RTL8366RB=m

The problem here is that the realtek-smi interface driver gets built-in,
while the rtl8366rb switch subdriver gets built as a module, hence the
symbol rtl8366rb_variant is not reachable when defining the OF device
table in the interface driver.

The Kconfig dependencies don't help in this scenario because they just
say that the subdriver(s) depend on at least one interface driver. In
fact, the subdrivers don't depend on the interface drivers at all, and
can even be built even in their absence. Somewhat strangely, the
interface drivers can also be built in the absence of any subdriver,
BUT, if a subdriver IS enabled, then it must be reachable according to
the linkage of the interface driver: effectively what the IS_REACHABLE()
macro achieves. If it is not reachable, the above kind of linker error
will be observed.

Rather than papering over the above build error by simply using
IS_REACHABLE(), we can do a little better and admit that it is actually
the interface drivers that have a dependency on the subdrivers. So this
patch does exactly that. Specifically, we ensure that:

1. The interface drivers' Kconfig symbols must have a value no greater
   than the value of any subdriver Kconfig symbols.

2. The subdrivers should by default enable both interface drivers, since
   most users probably want at least one of them; those interface
   drivers can be explicitly disabled however.

What this doesn't do is prevent a user from building only a subdriver,
without any interface driver. To that end, add an additional line of
help in the menu to guide users in the right direction.

Link: https://lore.kernel.org/all/202204110757.XIafvVnj-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Fixes: aac9400106 ("net: dsa: realtek: add new mdio interface for drivers")
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alvin Šipraga 2022-04-12 17:55:27 +02:00 committed by David S. Miller
parent dad32cfeed
commit 2511e0c877
1 changed files with 21 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
drivers/net/dsa/realtek/Kconfig
View File

@ -9,34 +9,46 @@ menuconfig NET_DSA_REALTEK
help
Select to enable support for Realtek Ethernet switch chips.
Note that at least one interface driver must be enabled for the
subdrivers to be loaded. Moreover, an interface driver cannot achieve
anything without at least one subdriver enabled.
if NET_DSA_REALTEK
config NET_DSA_REALTEK_MDIO
tristate "Realtek MDIO connected switch driver"
depends on NET_DSA_REALTEK
tristate "Realtek MDIO interface driver"
depends on OF
depends on NET_DSA_REALTEK_RTL8365MB || NET_DSA_REALTEK_RTL8366RB
depends on NET_DSA_REALTEK_RTL8365MB || !NET_DSA_REALTEK_RTL8365MB
depends on NET_DSA_REALTEK_RTL8366RB || !NET_DSA_REALTEK_RTL8366RB
help
Select to enable support for registering switches configured
through MDIO.
config NET_DSA_REALTEK_SMI
tristate "Realtek SMI connected switch driver"
depends on NET_DSA_REALTEK
tristate "Realtek SMI interface driver"
depends on OF
depends on NET_DSA_REALTEK_RTL8365MB || NET_DSA_REALTEK_RTL8366RB
depends on NET_DSA_REALTEK_RTL8365MB || !NET_DSA_REALTEK_RTL8365MB
depends on NET_DSA_REALTEK_RTL8366RB || !NET_DSA_REALTEK_RTL8366RB
help
Select to enable support for registering switches connected
through SMI.
config NET_DSA_REALTEK_RTL8365MB
tristate "Realtek RTL8365MB switch subdriver"
depends on NET_DSA_REALTEK
depends on NET_DSA_REALTEK_SMI || NET_DSA_REALTEK_MDIO
imply NET_DSA_REALTEK_SMI
imply NET_DSA_REALTEK_MDIO
select NET_DSA_TAG_RTL8_4
help
Select to enable support for Realtek RTL8365MB-VC and RTL8367S.
config NET_DSA_REALTEK_RTL8366RB
tristate "Realtek RTL8366RB switch subdriver"
depends on NET_DSA_REALTEK
depends on NET_DSA_REALTEK_SMI || NET_DSA_REALTEK_MDIO
imply NET_DSA_REALTEK_SMI
imply NET_DSA_REALTEK_MDIO
select NET_DSA_TAG_RTL4_A
help
Select to enable support for Realtek RTL8366RB
Select to enable support for Realtek RTL8366RB.
endif