net: stmmac: Prepare to add Split Header support

In order to add Split Header support, stmmac_rx() needs to take into
account that packet may be split accross multiple descriptors.

Refactor the logic of this function in order to support this scenario.

Changes from v2:
	- Fixup if condition detection (Jakub)
	- Don't stop NAPI with unfinished packet (Jakub)
	- Use napi_alloc_skb() (Jakub)
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -74,6 +74,12 @@ struct stmmac_rx_queue {
 	u32 rx_zeroc_thresh;
 	dma_addr_t dma_rx_phy;
 	u32 rx_tail_addr;
+	unsigned int state_saved;
+	struct {
+		struct sk_buff *skb;
+		unsigned int len;
+		unsigned int error;
+	} state;
 };
 
 struct stmmac_channel {

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3353,9 +3353,10 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 {
 	struct stmmac_rx_queue *rx_q = &priv->rx_queue[queue];
 	struct stmmac_channel *ch = &priv->channel[queue];
+	unsigned int count = 0, error = 0, len = 0;
+	int status = 0, coe = priv->hw->rx_csum;
 	unsigned int next_entry = rx_q->cur_rx;
-	int coe = priv->hw->rx_csum;
-	unsigned int count = 0;
+	struct sk_buff *skb = NULL;
 
 	if (netif_msg_rx_status(priv)) {
 		void *rx_head;
@@ -3369,10 +3370,28 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		stmmac_display_ring(priv, rx_head, DMA_RX_SIZE, true);
 	}
 	while (count < limit) {
+		enum pkt_hash_types hash_type;
 		struct stmmac_rx_buffer *buf;
+		unsigned int prev_len = 0;
 		struct dma_desc *np, *p;
-		int entry, status;
+		int entry;
+		u32 hash;
+
+		if (!count && rx_q->state_saved) {
+			skb = rx_q->state.skb;
+			error = rx_q->state.error;
+			len = rx_q->state.len;
+		} else {
+			rx_q->state_saved = false;
+			skb = NULL;
+			error = 0;
+			len = 0;
+		}
 
+		if (count >= limit)
+			break;
+
+read_again:
 		entry = next_entry;
 		buf = &rx_q->buf_pool[entry];
 
@@ -3407,29 +3426,25 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 			page_pool_recycle_direct(rx_q->page_pool, buf->page);
 			priv->dev->stats.rx_errors++;
 			buf->page = NULL;
-		} else {
-			enum pkt_hash_types hash_type;
-			struct sk_buff *skb;
-			unsigned int des;
-			int frame_len;
-			u32 hash;
-
-			stmmac_get_desc_addr(priv, p, &des);
-			frame_len = stmmac_get_rx_frame_len(priv, p, coe);
+			error = 1;
+		}
 
-			/*  If frame length is greater than skb buffer size
-			 *  (preallocated during init) then the packet is
-			 *  ignored
-			 */
-			if (frame_len > priv->dma_buf_sz) {
-				if (net_ratelimit())
-					netdev_err(priv->dev,
-						   "len %d larger than size (%d)\n",
-						   frame_len, priv->dma_buf_sz);
-				priv->dev->stats.rx_length_errors++;
+		if (unlikely(error && (status & rx_not_ls)))
+			goto read_again;
+		if (unlikely(error)) {
+			if (skb)
+				dev_kfree_skb(skb);
 			continue;
 		}
 
+		/* Buffer is good. Go on. */
+
+		if (likely(status & rx_not_ls)) {
+			len += priv->dma_buf_sz;
+		} else {
+			prev_len = len;
+			len = stmmac_get_rx_frame_len(priv, p, coe);
+
 			/* ACS is set; GMAC core strips PAD/FCS for IEEE 802.3
 			 * Type frames (LLC/LLC-SNAP)
 			 *
@@ -3439,37 +3454,49 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 			 */
 			if (unlikely(priv->synopsys_id >= DWMAC_CORE_4_00) ||
 			    unlikely(status != llc_snap))
-				frame_len -= ETH_FCS_LEN;
-
-			if (netif_msg_rx_status(priv)) {
-				netdev_dbg(priv->dev, "\tdesc: %p [entry %d] buff=0x%x\n",
-					   p, entry, des);
-				netdev_dbg(priv->dev, "frame size %d, COE: %d\n",
-					   frame_len, status);
+				len -= ETH_FCS_LEN;
 		}
 
-			skb = netdev_alloc_skb_ip_align(priv->dev, frame_len);
-			if (unlikely(!skb)) {
+		if (!skb) {
+			skb = napi_alloc_skb(&ch->rx_napi, len);
+			if (!skb) {
 				priv->dev->stats.rx_dropped++;
 				continue;
 			}
 
-			dma_sync_single_for_cpu(priv->device, buf->addr,
-						frame_len, DMA_FROM_DEVICE);
+			dma_sync_single_for_cpu(priv->device, buf->addr, len,
+						DMA_FROM_DEVICE);
 			skb_copy_to_linear_data(skb, page_address(buf->page),
-						frame_len);
-			skb_put(skb, frame_len);
+						len);
+			skb_put(skb, len);
 
-			if (netif_msg_pktdata(priv)) {
-				netdev_dbg(priv->dev, "frame received (%dbytes)",
-					   frame_len);
-				print_pkt(skb->data, frame_len);
+			/* Data payload copied into SKB, page ready for recycle */
+			page_pool_recycle_direct(rx_q->page_pool, buf->page);
+			buf->page = NULL;
+		} else {
+			unsigned int buf_len = len - prev_len;
+
+			if (likely(status & rx_not_ls))
+				buf_len = priv->dma_buf_sz;
+
+			dma_sync_single_for_cpu(priv->device, buf->addr,
+						buf_len, DMA_FROM_DEVICE);
+			skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
+					buf->page, 0, buf_len,
+					priv->dma_buf_sz);
+
+			/* Data payload appended into SKB */
+			page_pool_release_page(rx_q->page_pool, buf->page);
+			buf->page = NULL;
 		}
 
-			stmmac_get_rx_hwtstamp(priv, p, np, skb);
+		if (likely(status & rx_not_ls))
+			goto read_again;
 
-			stmmac_rx_vlan(priv->dev, skb);
+		/* Got entire packet into SKB. Finish it. */
 
+		stmmac_get_rx_hwtstamp(priv, p, np, skb);
+		stmmac_rx_vlan(priv->dev, skb);
 		skb->protocol = eth_type_trans(skb, priv->dev);
 
 		if (unlikely(!coe))
@@ -3483,13 +3510,15 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		skb_record_rx_queue(skb, queue);
 		napi_gro_receive(&ch->rx_napi, skb);
 
-			/* Data payload copied into SKB, page ready for recycle */
-			page_pool_recycle_direct(rx_q->page_pool, buf->page);
-			buf->page = NULL;
-
 		priv->dev->stats.rx_packets++;
-			priv->dev->stats.rx_bytes += frame_len;
+		priv->dev->stats.rx_bytes += len;
 	}
+
+	if (status & rx_not_ls) {
+		rx_q->state_saved = true;
+		rx_q->state.skb = skb;
+		rx_q->state.error = error;
+		rx_q->state.len = len;
 	}
 
 	stmmac_rx_refill(priv, queue);