[PATCH] /dev/dax: fix Kconfig dependency build breakage

[Ross Zwisler]

The function dax_pmem_probe() in drivers/dax/pmem.c is compiled under the
CONFIG_DEV_DAX_PMEM tri-state config option.  This config option currently
only depends on CONFIG_NVDIMM_DAX, which means that the following
configuration is possible:

CONFIG_LIBNVDIMM=m
...
CONFIG_NVDIMM_DAX=y
CONFIG_DEV_DAX=y
CONFIG_DEV_DAX_PMEM=y

With this config LIBNVDIMM is compiled as a module with NVDIMM_DAX=y just
meaning that we will compile drivers/nvdimm/dax_devs.c into that module.
However, dax_pmem_probe() depends on several symbols defined in
drivers/nvdimm/dax_devs.c, which results in the following build errors:

drivers/built-in.o: In function `dax_pmem_probe':
linux/drivers/dax/pmem.c:70: undefined reference to `to_nd_dax'
linux/drivers/dax/pmem.c:74: undefined reference to `nvdimm_namespace_common_probe'
linux/drivers/dax/pmem.c:80: undefined reference to `devm_nsio_enable'
linux/drivers/dax/pmem.c:81: undefined reference to `nvdimm_setup_pfn'
linux/drivers/dax/pmem.c:84: undefined reference to `devm_nsio_disable'
linux/drivers/dax/pmem.c:122: undefined reference to `to_nd_region'
drivers/built-in.o: In function `dax_pmem_init':
linux/drivers/dax/pmem.c:147: undefined reference to `__nd_driver_register'

Fix this by making CONFIG_DEV_DAX_PMEM explicitly depend on
CONFIG_LIBNVDIMM.  This prevents dax_devs.c from being built as a built-in
while its dependencies are in the libnvdimm.ko module.

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 drivers/dax/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index cedab75..5cd9436 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -15,6 +15,7 @@ if DEV_DAX
 config DEV_DAX_PMEM
 	tristate "PMEM DAX: direct access to persistent memory"
 	depends on NVDIMM_DAX
+	depends on LIBNVDIMM
 	default DEV_DAX
 	help
 	  Support raw access to persistent memory.  Note that this
-- 
2.9.0