[PATCH v4] vdpa: mlx5: fix vdpa/vhost dependencies

[Randy Dunlap]

drivers/vdpa/mlx5/ uses vhost_iotlb*() interfaces, so select
VHOST_IOTLB to make them be built.

However, if VHOST_IOTLB is the only VHOST symbol that is
set/enabled, the object file still won't be built because
drivers/Makefile won't descend into drivers/vhost/ to build it,
so make drivers/Makefile build the needed binary whenever
VHOST_IOTLB is set, like it does for VHOST_RING.

Fixes these build errors:
ERROR: modpost: "vhost_iotlb_itree_next" [drivers/vdpa/mlx5/mlx5_vdpa.ko] undefined!
ERROR: modpost: "vhost_iotlb_itree_first" [drivers/vdpa/mlx5/mlx5_vdpa.ko] undefined!

Fixes: 29064bfdabd5 ("vdpa/mlx5: Add support library for mlx5 VDPA implementation")
Fixes: aff90770e54c ("vdpa/mlx5: Fix dependency on MLX5_CORE")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Eli Cohen <eli@xxxxxxxxxxxx>
Cc: Parav Pandit <parav@xxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Saeed Mahameed <saeedm@xxxxxxxxxx>
Cc: Leon Romanovsky <leonro@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
---
v2: change from select to depends on VHOST (Saeed)
v3: change to depends on VHOST_IOTLB (Jason)
v4: use select VHOST_IOTLB (Michael); also add to drivers/Makefile

 drivers/Makefile     |    1 +
 drivers/vdpa/Kconfig |    1 +
 2 files changed, 2 insertions(+)

--- linux-next-20201127.orig/drivers/vdpa/Kconfig
+++ linux-next-20201127/drivers/vdpa/Kconfig
@@ -32,6 +32,7 @@ config IFCVF
 
 config MLX5_VDPA
 	bool
+	select VHOST_IOTLB
 	help
 	  Support library for Mellanox VDPA drivers. Provides code that is
 	  common for all types of VDPA drivers. The following drivers are planned:
--- linux-next-20201127.orig/drivers/Makefile
+++ linux-next-20201127/drivers/Makefile
@@ -143,6 +143,7 @@ obj-$(CONFIG_OF)		+= of/
 obj-$(CONFIG_SSB)		+= ssb/
 obj-$(CONFIG_BCMA)		+= bcma/
 obj-$(CONFIG_VHOST_RING)	+= vhost/
+obj-$(CONFIG_VHOST_IOTLB)	+= vhost/
 obj-$(CONFIG_VHOST)		+= vhost/
 obj-$(CONFIG_VLYNQ)		+= vlynq/
 obj-$(CONFIG_GREYBUS)		+= greybus/