Add helpers to register, queue and flush the deferred work.

These helpers allow dax_hmem to execute ownership resolution outside the
probe context before dax_cxl binds.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
---
 drivers/dax/bus.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
 drivers/dax/bus.h |  7 ++++++
 2 files changed, 65 insertions(+)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 5f387feb95f0..92b88952ede1 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -25,6 +25,64 @@ DECLARE_RWSEM(dax_region_rwsem);
  */
 DECLARE_RWSEM(dax_dev_rwsem);
 
+static DEFINE_MUTEX(dax_hmem_lock);
+static dax_hmem_deferred_fn hmem_deferred_fn;
+static void *dax_hmem_data;
+
+static void hmem_deferred_work(struct work_struct *work)
+{
+	dax_hmem_deferred_fn fn;
+	void *data;
+
+	scoped_guard(mutex, &dax_hmem_lock) {
+		fn = hmem_deferred_fn;
+		data = dax_hmem_data;
+	}
+
+	if (fn)
+		fn(data);
+}
+
+static DECLARE_WORK(dax_hmem_work, hmem_deferred_work);
+
+int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data)
+{
+	guard(mutex)(&dax_hmem_lock);
+
+	if (hmem_deferred_fn)
+		return -EINVAL;
+
+	hmem_deferred_fn = fn;
+	dax_hmem_data = data;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dax_hmem_register_work);
+
+int dax_hmem_unregister_work(dax_hmem_deferred_fn fn, void *data)
+{
+	guard(mutex)(&dax_hmem_lock);
+
+	if (hmem_deferred_fn != fn || dax_hmem_data != data)
+		return -EINVAL;
+
+	hmem_deferred_fn = NULL;
+	dax_hmem_data = NULL;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dax_hmem_unregister_work);
+
+void dax_hmem_queue_work(void)
+{
+	queue_work(system_long_wq, &dax_hmem_work);
+}
+EXPORT_SYMBOL_GPL(dax_hmem_queue_work);
+
+void dax_hmem_flush_work(void)
+{
+	flush_work(&dax_hmem_work);
+}
+EXPORT_SYMBOL_GPL(dax_hmem_flush_work);
+
 #define DAX_NAME_LEN 30
 struct dax_id {
 	struct list_head list;
diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
index cbbf64443098..b58a88e8089c 100644
--- a/drivers/dax/bus.h
+++ b/drivers/dax/bus.h
@@ -41,6 +41,13 @@ struct dax_device_driver {
 	void (*remove)(struct dev_dax *dev);
 };
 
+typedef void (*dax_hmem_deferred_fn)(void *data);
+
+int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data);
+int dax_hmem_unregister_work(dax_hmem_deferred_fn fn, void *data);
+void dax_hmem_queue_work(void);
+void dax_hmem_flush_work(void);
+
 int __dax_driver_register(struct dax_device_driver *dax_drv,
 		struct module *module, const char *mod_name);
 #define dax_driver_register(driver) \
-- 
2.17.1