[PATCH] net: mellanox: add DEVLINK dependencies

The new NET_DEVLINK infrastructure can be a loadable module, but the drivers
using it might be built-in, which causes link errors like:

drivers/net/built-in.o: In function `mlx4_load_one':
:(.text+0x2fbfda): undefined reference to `devlink_port_register'
:(.text+0x2fc084): undefined reference to `devlink_port_unregister'
drivers/net/built-in.o: In function `mlxsw_sx_port_remove':
:(.text+0x33a03a): undefined reference to `devlink_port_type_clear'
:(.text+0x33a04e): undefined reference to `devlink_port_unregister'

There are multiple ways to avoid this:

a) add 'depends on NET_DEVLINK || !NET_DEVLINK' dependencies
   for each user
b) use 'select NET_DEVLINK' from each driver that uses it
   and hide the symbol in Kconfig.
c) make NET_DEVLINK a 'bool' option so we don't have to
   list it as a dependency, and rely on the APIs to be
   stubbed out when it is disabled
d) use IS_REACHABLE() rather than IS_ENABLED() to check for
   NET_DEVLINK in include/net/devlink.h

This implements a variation of approach a) by adding an
intermediate symbol that drivers can depend on, and changes
the three drivers using it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 09d4d087cd48 ("mlx4: Implement devlink interface")
Fixes: c4745500e988 ("mlxsw: Implement devlink interface")
---
 drivers/infiniband/hw/mlx4/Kconfig          | 1 +
 drivers/net/ethernet/mellanox/mlx4/Kconfig  | 1 +
 drivers/net/ethernet/mellanox/mlxsw/Kconfig | 1 +
 net/Kconfig                                 | 9 +++++++++
 4 files changed, 12 insertions(+)

diff --git a/drivers/infiniband/hw/mlx4/Kconfig b/drivers/infiniband/hw/mlx4/Kconfig
index fc01deac1d3c..db4aa13ebae0 100644
--- a/drivers/infiniband/hw/mlx4/Kconfig
+++ b/drivers/infiniband/hw/mlx4/Kconfig

@@ -1,6 +1,7 @@
 config MLX4_INFINIBAND
 	tristate "Mellanox ConnectX HCA support"
 	depends on NETDEVICES && ETHERNET && PCI && INET
+	depends on MAY_USE_DEVLINK
 	select NET_VENDOR_MELLANOX
 	select MLX4_CORE
 	---help---

diff --git a/drivers/net/ethernet/mellanox/mlx4/Kconfig b/drivers/net/ethernet/mellanox/mlx4/Kconfig
index 1486ce902a56..9ca3734ebb6b 100644
--- a/drivers/net/ethernet/mellanox/mlx4/Kconfig
+++ b/drivers/net/ethernet/mellanox/mlx4/Kconfig

@@ -4,6 +4,7 @@
 
 config MLX4_EN
 	tristate "Mellanox Technologies 1/10/40Gbit Ethernet support"
+	depends on MAY_USE_DEVLINK
 	depends on PCI
 	select MLX4_CORE
 	select PTP_1588_CLOCK

diff --git a/drivers/net/ethernet/mellanox/mlxsw/Kconfig b/drivers/net/ethernet/mellanox/mlxsw/Kconfig
index ce26adcb4988..2ad7f67854d5 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/Kconfig
+++ b/drivers/net/ethernet/mellanox/mlxsw/Kconfig

@@ -4,6 +4,7 @@
 
 config MLXSW_CORE
 	tristate "Mellanox Technologies Switch ASICs support"
+	depends on MAY_USE_DEVLINK
 	---help---
 	  This driver supports Mellanox Technologies Switch ASICs family.
 

diff --git a/net/Kconfig b/net/Kconfig
index 6c9cfb0d7639..2760825e53fa 100644
--- a/net/Kconfig
+++ b/net/Kconfig

@@ -403,6 +403,15 @@ config NET_DEVLINK
 	  infrastructure to support access to physical chip-wide config and
 	  monitoring.
 
+config MAY_USE_DEVLINK
+	tristate
+	default m if NET_DEVLINK=m
+	default y if NET_DEVLINK=y || NET_DEVLINK=n
+	help
+	  Drivers using the devlink infrastructure should have a dependency
+	  on MAY_USE_DEVLINK to ensure they do not cause link errors when
+	  devlink is a loadable module and the driver using it is built-in.
+
 endif   # if NET
 
 # Used by archs to tell that they support BPF_JIT

-- 
2.7.0

Wed, Mar 02, 2016 at 10:40:54AM CET, arnd at arndb.de wrote:

The new NET_DEVLINK infrastructure can be a loadable module, but the drivers
using it might be built-in, which causes link errors like:

drivers/net/built-in.o: In function `mlx4_load_one':
:(.text+0x2fbfda): undefined reference to `devlink_port_register'
:(.text+0x2fc084): undefined reference to `devlink_port_unregister'
drivers/net/built-in.o: In function `mlxsw_sx_port_remove':
:(.text+0x33a03a): undefined reference to `devlink_port_type_clear'
:(.text+0x33a04e): undefined reference to `devlink_port_unregister'

There are multiple ways to avoid this:

a) add 'depends on NET_DEVLINK || !NET_DEVLINK' dependencies
  for each user
b) use 'select NET_DEVLINK' from each driver that uses it
  and hide the symbol in Kconfig.
c) make NET_DEVLINK a 'bool' option so we don't have to
  list it as a dependency, and rely on the APIs to be
  stubbed out when it is disabled
d) use IS_REACHABLE() rather than IS_ENABLED() to check for
  NET_DEVLINK in include/net/devlink.h

This implements a variation of approach a) by adding an
intermediate symbol that drivers can depend on, and changes
the three drivers using it.

Approach a) looks like the best. Thanks for taking care of this.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Jiri Pirko <redacted>

From: Arnd Bergmann <arnd@arndb.de>
Date: Wed,  2 Mar 2016 10:40:54 +0100

The new NET_DEVLINK infrastructure can be a loadable module, but the drivers
using it might be built-in, which causes link errors like:

drivers/net/built-in.o: In function `mlx4_load_one':
:(.text+0x2fbfda): undefined reference to `devlink_port_register'
:(.text+0x2fc084): undefined reference to `devlink_port_unregister'
drivers/net/built-in.o: In function `mlxsw_sx_port_remove':
:(.text+0x33a03a): undefined reference to `devlink_port_type_clear'
:(.text+0x33a04e): undefined reference to `devlink_port_unregister'

There are multiple ways to avoid this:

a) add 'depends on NET_DEVLINK || !NET_DEVLINK' dependencies
   for each user
b) use 'select NET_DEVLINK' from each driver that uses it
   and hide the symbol in Kconfig.
c) make NET_DEVLINK a 'bool' option so we don't have to
   list it as a dependency, and rely on the APIs to be
   stubbed out when it is disabled
d) use IS_REACHABLE() rather than IS_ENABLED() to check for
   NET_DEVLINK in include/net/devlink.h

This implements a variation of approach a) by adding an
intermediate symbol that drivers can depend on, and changes
the three drivers using it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 09d4d087cd48 ("mlx4: Implement devlink interface")
Fixes: c4745500e988 ("mlxsw: Implement devlink interface")

Applied, thanks Arnd.