list: import list_first_entry_or_null()

Import list_first_entry_or_null() macro from Linux that would be used
by Cadence USB driver

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>

diff --git a/include/linux/list.h b/include/linux/list.h
index 5b8d1df..f62afa0 100644 (file)
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -349,6 +349,20 @@ static inline void list_splice_tail_init(struct list_head *list,
        list_entry((ptr)->prev, type, member)
 
 /**
+ * list_first_entry_or_null - get the first element from a list
+ * @ptr:       the list head to take the element from.
+ * @type:      the type of the struct this is embedded in.
+ * @member:    the name of the list_head within the struct.
+ *
+ * Note that if the list is empty, it returns NULL.
+ */
+#define list_first_entry_or_null(ptr, type, member) ({ \
+       struct list_head *head__ = (ptr); \
+       struct list_head *pos__ = READ_ONCE(head__->next); \
+       pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
+
+/**
  * list_for_each       -       iterate over a list
  * @pos:       the &struct list_head to use as a loop cursor.
  * @head:      the head for your list.