Merge patch series "list.h/treewide: get rid of no-op prefetch()"

Rasmus Villemoes <ravi@prevas.dk> says:

While looking through list.h, I saw that the regular list_* helpers
(and one of the hlist_* ones) still contain the prefetch() that was
removed in linux 14 years ago. It doesn't do anything, but makes the
macros harder to read, so get rid of it, and the fallback, no-op
definition that they relied on. That requires removing a few uses
outside list.h as well.

checkpatch warns about some whitespace issues in list.h, but as I've
copied whole kerneldoc+#define blocks directly from the linux kernel,
I think it's better to just accept that so that we don't introduce
needless diffs. The "macro argument reuse" arguments should also be
ignored, as e.g. the "member" arguments are obviously always just bare
identifiers, and the "pos" arguments must be assigned to multiple
times.

Link: https://lore.kernel.org/r/20250507121246.518691-1-ravi@prevas.dk

arch/mips/include/asm/processor.h

@@ -118,20 +118,4 @@ struct task_struct;
  */
 #define return_address() ({__asm__ __volatile__("":::"$31");__builtin_return_address(0);})
 
-#ifdef CONFIG_CPU_HAS_PREFETCH
-
-#define ARCH_HAS_PREFETCH
-
-static inline void prefetch(const void *addr)
-{
-	__asm__ __volatile__(
-	"	.set	mips4		\n"
-	"	pref	%0, (%1)	\n"
-	"	.set	mips0		\n"
-	:
-	: "i" (Pref_Load), "r" (addr));
-}
-
-#endif
-
 #endif /* _ASM_PROCESSOR_H */

drivers/net/mvpp2.c

@@ -3876,7 +3876,6 @@ mvpp2_rxq_next_desc_get(struct mvpp2_rx_queue *rxq)
 	int rx_desc = rxq->next_desc_to_proc;
 
 	rxq->next_desc_to_proc = MVPP2_QUEUE_NEXT_DESC(rxq, rx_desc);
-	prefetch(rxq->descs + rxq->next_desc_to_proc);
 	return rxq->descs + rx_desc;
 }
 

drivers/net/octeontx/nicvf_main.c

@@ -279,8 +279,6 @@ int nicvf_cq_handler(struct nicvf *nic, void **ppkt, int *pkt_len)
 		cq_desc = (struct cqe_rx_t *)GET_CQ_DESC(cq, cqe_head);
 		cqe_head++;
 		cqe_head &= (cq->dmem.q_len - 1);
-		/* Initiate prefetch for next descriptor */
-		prefetch((struct cqe_rx_t *)GET_CQ_DESC(cq, cqe_head));
 
 		switch (cq_desc->cqe_type) {
 		case CQE_TYPE_RX:

drivers/usb/gadget/at91_udc.c

@@ -228,7 +228,6 @@ static int write_fifo(struct at91_ep *ep, struct at91_request *req)
 	}
 
 	buf = req->req.buf + req->req.actual;
-	prefetch(buf);
 	total = req->req.length - req->req.actual;
 	if (ep->ep.maxpacket < total) {
 		count = ep->ep.maxpacket;

drivers/usb/musb-new/musb_core.c

@@ -223,8 +223,6 @@ void musb_write_fifo(struct musb_hw_ep *hw_ep, u16 len, const u8 *src)
 	struct musb *musb = hw_ep->musb;
 	void __iomem *fifo = hw_ep->fifo;
 
-	prefetch((u8 *)src);
-
 	dev_dbg(musb->controller, "%cX ep%d fifo %p count %d buf %p\n",
 			'T', hw_ep->epnum, fifo, len, src);
 

include/linux/list.h

@@ -4,11 +4,6 @@
 #include <linux/stddef.h>
 #include <linux/poison.h>
 
-#ifndef ARCH_HAS_PREFETCH
-#define ARCH_HAS_PREFETCH
-static inline void prefetch(const void *x) {;}
-#endif
-
 /*
  * Simple doubly linked list implementation.
  *
@@ -169,6 +164,16 @@ 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.
@@ -362,27 +367,29 @@ static inline void list_splice_tail_init(struct list_head *list,
 	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
 })
 
+/**
+ * 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_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
  * @pos:	the &struct list_head to use as a loop cursor.
  * @head:	the head for your list.
  */
 #define list_for_each(pos, head) \
-	for (pos = (head)->next; prefetch(pos->next), pos != (head); \
-		pos = pos->next)
-
-/**
- * __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)
+	for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)
 
 /**
  * list_for_each_prev	-	iterate over a list backwards
@@ -390,8 +397,7 @@ 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 +417,39 @@ 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 +466,41 @@ 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 +669,7 @@ 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; }); \