Introduce a global "DAX Regions" resource root and register each
dax_region->res under it via request_resource(). Release the resource on
dax_region teardown.

By enforcing a single global namespace for dax_region allocations, this
ensures only one of dax_hmem or dax_cxl can successfully register a
dax_region for a given range.

Co-developed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
---
 drivers/dax/bus.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index fde29e0ad68b..5f387feb95f0 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -10,6 +10,7 @@
 #include "dax-private.h"
 #include "bus.h"
 
+static struct resource dax_regions = DEFINE_RES_MEM_NAMED(0, -1, "DAX Regions");
 static DEFINE_MUTEX(dax_bus_lock);
 
 /*
@@ -625,6 +626,8 @@ static void dax_region_unregister(void *region)
 {
 	struct dax_region *dax_region = region;
 
+	scoped_guard(rwsem_write, &dax_region_rwsem)
+		release_resource(&dax_region->res);
 	sysfs_remove_groups(&dax_region->dev->kobj,
 			dax_region_attribute_groups);
 	dax_region_put(dax_region);
@@ -635,6 +638,7 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		unsigned long flags)
 {
 	struct dax_region *dax_region;
+	int rc;
 
 	/*
 	 * The DAX core assumes that it can store its private data in
@@ -667,14 +671,27 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		.flags = IORESOURCE_MEM | flags,
 	};
 
-	if (sysfs_create_groups(&parent->kobj, dax_region_attribute_groups)) {
-		kfree(dax_region);
-		return NULL;
+	scoped_guard(rwsem_write, &dax_region_rwsem)
+		rc = request_resource(&dax_regions, &dax_region->res);
+	if (rc) {
+		dev_dbg(parent, "dax_region resource conflict for %pR\n",
+			&dax_region->res);
+		goto err_res;
 	}
 
+	if (sysfs_create_groups(&parent->kobj, dax_region_attribute_groups))
+		goto err_sysfs;
+
 	if (devm_add_action_or_reset(parent, dax_region_unregister, dax_region))
 		return NULL;
 	return dax_region;
+
+err_sysfs:
+	scoped_guard(rwsem_write, &dax_region_rwsem)
+		release_resource(&dax_region->res);
+err_res:
+	kfree(dax_region);
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(alloc_dax_region);
 
-- 
2.17.1