mm/memory_hotplug: export mhp_get_default_online_type

Drivers which may pass hotplug policy down to DAX need MMOP_ symbols and
the mhp_get_default_online_type function for hotplug use cases.

Some drivers (cxl) co-mingle their hotplug and devdax use-cases into the
same driver code, and chose the dax_kmem path as the default driver path -
making it difficult to require hotplug as a predicate to building the
overall driver (it may break other non-hotplug use-cases).

Export mhp_get_default_online_type function to allow these drivers to
build when hotplug is disabled and still use the DAX use case.

In the built-out case we simply return MMOP_OFFLINE as it's
non-destructive.  The internal function can never return -1 either, so we
choose this to allow for defining the function with 'enum mmop'.

Link: https://lore.kernel.org/20260712154505.3564379-5-gourry@gourry.net
Signed-off-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Dan Williams <djbw@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pankaj Gupta <pankaj.gupta@amd.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 3f5d63892d90..5240aa28bc90 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -317,6 +317,8 @@ extern struct zone *zone_for_pfn_range(enum mmop online_type,
 extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
 				      struct mhp_params *params);
 void arch_remove_linear_mapping(u64 start, u64 size);
+#else
+static inline enum mmop mhp_get_default_online_type(void) { return MMOP_OFFLINE; }
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
 #endif /* __LINUX_MEMORY_HOTPLUG_H */