[PATCH 6/6] net: macb: rework macb_tx_complete() processing loop

["Théo Lebrun" <theo.lebrun@bootlin.com>]

The SKB case of macb_tx_complete() must iterate over buffers taking into
account frames might be multi-buffer. Following that, the code for XDP
got integrated into the same loop. But in XDP cases, frames must be
single buffer.

Knowing that, we reverse operations: first we check the buffer type,
then we iterate to consume all frame buffers if it is an SKB buffer.

Side-effects:

 - Statistics tx_packets and tx_bytes are now incremented for
   XDP_TX and XDP_NDO frames as well.

 - Only increment statistics once per macb_tx_complete() call rather
   than once per frame.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/net/ethernet/cadence/macb_main.c | 71 +++++++++++-------------
 1 file changed, 33 insertions(+), 38 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 2c7644f2215a..6c33af667405 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -1202,11 +1202,10 @@ static int macb_tx_complete(struct macb_queue *queue, int budget)
 	spin_lock_irqsave(&queue->tx_ptr_lock, flags);
 	head = queue->tx_head;
 	for (tail = queue->tx_tail; tail != head && packets < budget; tail++) {
-		void			*data = NULL;
-		struct macb_tx_buff	*tx_buff;
-		struct sk_buff		*skb;
-		struct macb_dma_desc	*desc;
-		u32			ctrl;
+		struct macb_tx_buff *tx_buff;
+		struct macb_dma_desc *desc;
+		struct sk_buff *skb;
+		u32 ctrl;
 
 		desc = macb_tx_desc(queue, tail);
 
@@ -1221,48 +1220,44 @@ static int macb_tx_complete(struct macb_queue *queue, int budget)
 		if (!(ctrl & MACB_BIT(TX_USED)))
 			break;
 
-		/* Process all buffers of the current transmitted frame */
-		for (;; tail++) {
-			tx_buff = macb_tx_buff(queue, tail);
+		tx_buff = macb_tx_buff(queue, tail);
 
-			if (tx_buff->type != MACB_TYPE_SKB) {
-				data = tx_buff->ptr;
-				goto unmap;
+		switch (tx_buff->type) {
+		case MACB_TYPE_SKB:
+			/* Process all buffers of the current transmitted frame */
+			while (!tx_buff->ptr) {
+				macb_tx_unmap(bp, tx_buff, budget);
+				tail++;
+				tx_buff = macb_tx_buff(queue, tail);
 			}
 
-			/* First, update TX stats if needed */
-			if (tx_buff->type == MACB_TYPE_SKB && tx_buff->ptr) {
-				data = tx_buff->ptr;
-				skb = tx_buff->ptr;
+			skb = tx_buff->ptr;
 
-				if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
-				    !ptp_one_step_sync(skb))
-					gem_ptp_do_txstamp(bp, skb, desc);
+			if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
+			    !ptp_one_step_sync(skb))
+				gem_ptp_do_txstamp(bp, skb, desc);
 
-				netdev_vdbg(bp->dev, "skb %u (data %p) TX complete\n",
-					    macb_tx_ring_wrap(bp, tail),
-					    skb->data);
-				bp->dev->stats.tx_packets++;
-				queue->stats.tx_packets++;
-				bp->dev->stats.tx_bytes += skb->len;
-				queue->stats.tx_bytes += skb->len;
-				packets++;
-				bytes += skb->len;
-			}
+			netdev_vdbg(bp->dev, "skb %u (data %p) TX complete\n",
+				    macb_tx_ring_wrap(bp, tail),
+				    skb->data);
+			bytes += skb->len;
+			break;
 
-unmap:
-			/* Now we can safely release resources */
-			macb_tx_unmap(bp, tx_buff, budget);
-
-			/* skb is set only for the last buffer of the frame.
-			 * WARNING: at this point skb has been freed by
-			 * macb_tx_unmap().
-			 */
-			if (data)
-				break;
+		case MACB_TYPE_XDP_TX:
+		case MACB_TYPE_XDP_NDO:
+			bytes += tx_buff->size;
+			break;
 		}
+
+		packets++;
+		macb_tx_unmap(bp, tx_buff, budget);
 	}
 
+	bp->dev->stats.tx_packets += packets;
+	queue->stats.tx_packets += packets;
+	bp->dev->stats.tx_bytes += bytes;
+	queue->stats.tx_bytes += bytes;
+
 	netdev_tx_completed_queue(netdev_get_tx_queue(bp->dev, queue_index),
 				  packets, bytes);
 
-- 
2.53.0