cxl/region: Limit visibility of cxl_region_contains_resource()

The dax_hmem dependency on cxl_region_contains_resource() is a one-off
special case. It is not suitable for other use cases.

Move the definition to the other CONFIG_CXL_REGION guarded definitions in
drivers/cxl/cxl.h and include that by a relative path include. This matches
what drivers/dax/cxl.c does for its limited private usage of CXL core
symbols.

Reduce the symbol export visibility from global to just dax_hmem, to
further clarify its applicability.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://patch.msgid.link/20260327052821.440749-4-dan.j.williams@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Author: djbw

drivers/cxl/core/region.c

@@ -12,7 +12,6 @@
 #include <linux/idr.h>
 #include <linux/memory-tiers.h>
 #include <linux/string_choices.h>
-#include <cxl/cxl.h>
 #include <cxlmem.h>
 #include <cxl.h>
 #include "core.h"
@@ -4253,7 +4252,7 @@ bool cxl_region_contains_resource(struct resource *res)
 	return bus_for_each_dev(&cxl_bus_type, NULL, res,
 				region_contains_resource) != 0;
 }
-EXPORT_SYMBOL_GPL(cxl_region_contains_resource);
+EXPORT_SYMBOL_FOR_MODULES(cxl_region_contains_resource, "dax_hmem");
 
 static int cxl_region_can_probe(struct cxl_region *cxlr)
 {

drivers/cxl/cxl.h

@@ -941,6 +941,7 @@ struct cxl_pmem_region *to_cxl_pmem_region(struct device *dev);
 int cxl_add_to_region(struct cxl_endpoint_decoder *cxled);
 struct cxl_dax_region *to_cxl_dax_region(struct device *dev);
 u64 cxl_port_get_spa_cache_alias(struct cxl_port *endpoint, u64 spa);
+bool cxl_region_contains_resource(struct resource *res);
 #else
 static inline bool is_cxl_pmem_region(struct device *dev)
 {
@@ -963,6 +964,10 @@ static inline u64 cxl_port_get_spa_cache_alias(struct cxl_port *endpoint,
 {
 	return 0;
 }
+static inline bool cxl_region_contains_resource(struct resource *res)
+{
+	return false;
+}
 #endif
 
 void cxl_endpoint_parse_cdat(struct cxl_port *port);

drivers/dax/hmem/hmem.c

@@ -3,7 +3,7 @@
 #include <linux/memregion.h>
 #include <linux/module.h>
 #include <linux/dax.h>
-#include <cxl/cxl.h>
+#include "../../cxl/cxl.h"
 #include "../bus.h"
 
 static bool region_idle;