[PATCH 1/4] linux/list.h: drop use of prefetch()

[Rasmus Villemoes]

The use of prefetch() in these list helpers was dropped back in 2011
in linux (e66eed651fd1 ("list: remove prefetching from regular list
iterators")). No arch in U-Boot defines any actual prefetch(), and as
the referenced commit says, it's usually not a win anyway.

Whole-sale sync of list.h is not really feasible, but we can
synchronize the macros containing a prefetch() with their linux
implementations as of v6.15-rc5, also importing the various helpers
needed, e.g. list_is_head() and list_next_entry().

Signed-off-by: Rasmus Villemoes <ravi at prevas.dk>
---
 include/linux/list.h | 99 ++++++++++++++++++++++++++------------------
 1 file changed, 59 insertions(+), 40 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index 0f9d939b05f..e21ae03b208 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -169,6 +169,16 @@ static inline int list_is_last(const struct list_head *list,
 	return list->next == head;
 }
 
+/**
+ * list_is_head - tests whether @list is the list @head
+ * @list: the entry to test
+ * @head: the head of the list
+ */
+static inline int list_is_head(const struct list_head *list, const struct list_head *head)
+{
+	return list == head;
+}
+
 /**
  * list_empty - tests whether a list is empty
  * @head: the list to test.
@@ -363,26 +373,28 @@ static inline void list_splice_tail_init(struct list_head *list,
 })
 
 /**
- * list_for_each	-	iterate over a list
- * @pos:	the &struct list_head to use as a loop cursor.
- * @head:	the head for your list.
+ * list_next_entry - get the next element in list
+ * @pos:	the type * to cursor
+ * @member:	the name of the list_head within the struct.
  */
-#define list_for_each(pos, head) \
-	for (pos = (head)->next; prefetch(pos->next), pos != (head); \
-		pos = pos->next)
+#define list_next_entry(pos, member) \
+	list_entry((pos)->member.next, typeof(*(pos)), member)
+
+/**
+ * list_prev_entry - get the prev element in list
+ * @pos:	the type * to cursor
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_prev_entry(pos, member) \
+	list_entry((pos)->member.prev, typeof(*(pos)), member)
 
 /**
- * __list_for_each	-	iterate over a list
+ * list_for_each	-	iterate over a list
  * @pos:	the &struct list_head to use as a loop cursor.
  * @head:	the head for your list.
- *
- * This variant differs from list_for_each() in that it's the
- * simplest possible list iteration code, no prefetching is done.
- * Use this for code that knows the list to be very short (empty
- * or 1 entry) most of the time.
  */
-#define __list_for_each(pos, head) \
-	for (pos = (head)->next; pos != (head); pos = pos->next)
+#define list_for_each(pos, head) \
+	for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)
 
 /**
  * list_for_each_prev	-	iterate over a list backwards
@@ -390,8 +402,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * @head:	the head for your list.
  */
 #define list_for_each_prev(pos, head) \
-	for (pos = (head)->prev; prefetch(pos->prev), pos != (head); \
-		pos = pos->prev)
+	for (pos = (head)->prev; !list_is_head(pos, (head)); pos = pos->prev)
 
 /**
  * list_for_each_safe - iterate over a list safe against removal of list entry
@@ -411,30 +422,39 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_prev_safe(pos, n, head) \
 	for (pos = (head)->prev, n = pos->prev; \
-	     prefetch(pos->prev), pos != (head); \
+	     !list_is_head(pos, (head)); \
 	     pos = n, n = pos->prev)
 
+/**
+ * list_entry_is_head - test if the entry points to the head of the list
+ * @pos:	the type * to cursor
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_entry_is_head(pos, head, member)				\
+	list_is_head(&pos->member, (head))
+
 /**
  * list_for_each_entry	-	iterate over list of given type
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
+ * @member:	the name of the list_head within the struct.
  */
 #define list_for_each_entry(pos, head, member)				\
-	for (pos = list_entry((head)->next, typeof(*pos), member);	\
-	     prefetch(pos->member.next), &pos->member != (head);	\
-	     pos = list_entry(pos->member.next, typeof(*pos), member))
+	for (pos = list_first_entry(head, typeof(*pos), member);	\
+	     !list_entry_is_head(pos, head, member);			\
+	     pos = list_next_entry(pos, member))
 
 /**
  * list_for_each_entry_reverse - iterate backwards over list of given type.
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
+ * @member:	the name of the list_head within the struct.
  */
 #define list_for_each_entry_reverse(pos, head, member)			\
-	for (pos = list_entry((head)->prev, typeof(*pos), member);	\
-	     prefetch(pos->member.prev), &pos->member != (head);	\
-	     pos = list_entry(pos->member.prev, typeof(*pos), member))
+	for (pos = list_last_entry(head, typeof(*pos), member);		\
+	     !list_entry_is_head(pos, head, member); 			\
+	     pos = list_prev_entry(pos, member))
 
 /**
  * list_prepare_entry - prepare a pos entry for use in list_for_each_entry_continue()
@@ -451,41 +471,41 @@ static inline void list_splice_tail_init(struct list_head *list,
  * list_for_each_entry_continue - continue iteration over list of given type
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
+ * @member:	the name of the list_head within the struct.
  *
  * Continue to iterate over list of given type, continuing after
  * the current position.
  */
-#define list_for_each_entry_continue(pos, head, member)			\
-	for (pos = list_entry(pos->member.next, typeof(*pos), member);	\
-	     prefetch(pos->member.next), &pos->member != (head);	\
-	     pos = list_entry(pos->member.next, typeof(*pos), member))
+#define list_for_each_entry_continue(pos, head, member) 		\
+	for (pos = list_next_entry(pos, member);			\
+	     !list_entry_is_head(pos, head, member);			\
+	     pos = list_next_entry(pos, member))
 
 /**
  * list_for_each_entry_continue_reverse - iterate backwards from the given point
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
+ * @member:	the name of the list_head within the struct.
  *
  * Start to iterate over list of given type backwards, continuing after
  * the current position.
  */
 #define list_for_each_entry_continue_reverse(pos, head, member)		\
-	for (pos = list_entry(pos->member.prev, typeof(*pos), member);	\
-	     prefetch(pos->member.prev), &pos->member != (head);	\
-	     pos = list_entry(pos->member.prev, typeof(*pos), member))
+	for (pos = list_prev_entry(pos, member);			\
+	     !list_entry_is_head(pos, head, member);			\
+	     pos = list_prev_entry(pos, member))
 
 /**
  * list_for_each_entry_from - iterate over list of given type from the current point
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
+ * @member:	the name of the list_head within the struct.
  *
  * Iterate over list of given type, continuing from current position.
  */
-#define list_for_each_entry_from(pos, head, member)			\
-	for (; prefetch(pos->member.next), &pos->member != (head);	\
-	     pos = list_entry(pos->member.next, typeof(*pos), member))
+#define list_for_each_entry_from(pos, head, member) 			\
+	for (; !list_entry_is_head(pos, head, member);			\
+	     pos = list_next_entry(pos, member))
 
 /**
  * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
@@ -654,8 +674,7 @@ static inline void hlist_add_after(struct hlist_node *n,
 #define hlist_entry(ptr, type, member) container_of(ptr,type,member)
 
 #define hlist_for_each(pos, head) \
-	for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \
-	     pos = pos->next)
+	for (pos = (head)->first; pos ; pos = pos->next)
 
 #define hlist_for_each_safe(pos, n, head) \
 	for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \
-- 
2.49.0