mm/hmm: make HMM_MIRROR an implicit option

Make HMM_MIRROR an option that is selected by drivers wanting to use it
instead of a user visible option as it is just a low-level implementation
detail.

Link: https://lore.kernel.org/r/20190806160554.14046-15-hch@lst.deSigned-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>

drivers/gpu/drm/amd/amdgpu/Kconfig

@@ -27,7 +27,9 @@ config DRM_AMDGPU_CIK
 config DRM_AMDGPU_USERPTR
 	bool "Always enable userptr write support"
 	depends on DRM_AMDGPU
-	depends on HMM_MIRROR
+	depends on MMU
+	select HMM_MIRROR
+	select MMU_NOTIFIER
 	help
 	  This option selects CONFIG_HMM and CONFIG_HMM_MIRROR if it
 	  isn't already selected to enabled full userptr support.

drivers/gpu/drm/nouveau/Kconfig

@@ -86,9 +86,11 @@ config DRM_NOUVEAU_SVM
 	bool "(EXPERIMENTAL) Enable SVM (Shared Virtual Memory) support"
 	depends on DEVICE_PRIVATE
 	depends on DRM_NOUVEAU
-	depends on HMM_MIRROR
+	depends on MMU
 	depends on STAGING
+	select HMM_MIRROR
 	select MIGRATE_VMA_HELPER
+	select MMU_NOTIFIER
 	default n
 	help
 	  Say Y here if you want to enable experimental support for

mm/Kconfig

@@ -675,16 +675,14 @@ config MIGRATE_VMA_HELPER
 config DEV_PAGEMAP_OPS
 	bool
 
+#
+# Helpers to mirror range of the CPU page tables of a process into device page
+# tables.
+#
 config HMM_MIRROR
-	bool "HMM mirror CPU page table into a device page table"
+	bool
 	depends on MMU
-	select MMU_NOTIFIER
-	help
-	  Select HMM_MIRROR if you want to mirror range of the CPU page table of a
-	  process into a device page table. Here, mirror means "keep synchronized".
-	  Prerequisites: the device must provide the ability to write-protect its
-	  page tables (at PAGE_SIZE granularity), and must be able to recover from
-	  the resulting potential page faults.
+	depends on MMU_NOTIFIER
 
 config DEVICE_PRIVATE
 	bool "Unaddressable device memory (GPU memory, ...)"