net: mvneta: rely on build_skb in mvneta_rx_swbm poll routine

Refactor mvneta_rx_swbm code introducing mvneta_swbm_rx_frame and
mvneta_swbm_add_rx_fragment routines. Rely on build_skb in oreder to
allocate skb since the previous patch introduced buffer recycling using
the page_pool API.
This patch fixes even an issue in the original driver where dma buffers
are accessed before dma sync.
mvneta driver can run on not cache coherent devices so it is
necessary to sync DMA buffers before sending them to the device
in order to avoid memory corruptions. Running perf analysis we can
see a performance cost associated with this DMA-sync (anyway it is
already there in the original driver code). In follow up patches we
will add more logic to reduce DMA-sync as much as possible.
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -323,6 +323,11 @@
 	      ETH_HLEN + ETH_FCS_LEN,			     \
 	      cache_line_size())
 
+#define MVNETA_SKB_PAD	(SKB_DATA_ALIGN(sizeof(struct skb_shared_info) + \
+			 NET_SKB_PAD))
+#define MVNETA_SKB_SIZE(len)	(SKB_DATA_ALIGN(len) + MVNETA_SKB_PAD)
+#define MVNETA_MAX_RX_BUF_SIZE	(PAGE_SIZE - MVNETA_SKB_PAD)
+
 #define IS_TSO_HEADER(txq, addr) \
 	((addr >= txq->tso_hdrs_phys) && \
 	 (addr < txq->tso_hdrs_phys + txq->size * TSO_HEADER_SIZE))
@@ -646,7 +651,6 @@ static int txq_number = 8;
 static int rxq_def;
 
 static int rx_copybreak __read_mostly = 256;
-static int rx_header_size __read_mostly = 128;
 
 /* HW BM need that each port be identify by a unique ID */
 static int global_port_id;
@@ -1829,7 +1833,7 @@ static int mvneta_rx_refill(struct mvneta_port *pp,
 	phys_addr = page_pool_get_dma_addr(page) + pp->rx_offset_correction;
 	dma_dir = page_pool_get_dma_dir(rxq->page_pool);
 	dma_sync_single_for_device(pp->dev->dev.parent, phys_addr,
-				   PAGE_SIZE, dma_dir);
+				   MVNETA_MAX_RX_BUF_SIZE, dma_dir);
 	mvneta_rx_desc_fill(rx_desc, phys_addr, page, rxq);
 
 	return 0;
@@ -1947,30 +1951,102 @@ int mvneta_rx_refill_queue(struct mvneta_port *pp, struct mvneta_rx_queue *rxq)
 	return i;
 }
 
+static int
+mvneta_swbm_rx_frame(struct mvneta_port *pp,
+		     struct mvneta_rx_desc *rx_desc,
+		     struct mvneta_rx_queue *rxq,
+		     struct page *page)
+{
+	unsigned char *data = page_address(page);
+	int data_len = -MVNETA_MH_SIZE, len;
+	struct net_device *dev = pp->dev;
+	enum dma_data_direction dma_dir;
+
+	if (MVNETA_SKB_SIZE(rx_desc->data_size) > PAGE_SIZE) {
+		len = MVNETA_MAX_RX_BUF_SIZE;
+		data_len += len;
+	} else {
+		len = rx_desc->data_size;
+		data_len += len - ETH_FCS_LEN;
+	}
+
+	dma_dir = page_pool_get_dma_dir(rxq->page_pool);
+	dma_sync_single_for_cpu(dev->dev.parent,
+				rx_desc->buf_phys_addr,
+				len, dma_dir);
+
+	rxq->skb = build_skb(data, PAGE_SIZE);
+	if (unlikely(!rxq->skb)) {
+		netdev_err(dev,
+			   "Can't allocate skb on queue %d\n",
+			   rxq->id);
+		dev->stats.rx_dropped++;
+		rxq->skb_alloc_err++;
+		return -ENOMEM;
+	}
+	page_pool_release_page(rxq->page_pool, page);
+
+	skb_reserve(rxq->skb, MVNETA_MH_SIZE + NET_SKB_PAD);
+	skb_put(rxq->skb, data_len);
+	mvneta_rx_csum(pp, rx_desc->status, rxq->skb);
+
+	rxq->left_size = rx_desc->data_size - len;
+	rx_desc->buf_phys_addr = 0;
+
+	return 0;
+}
+
+static void
+mvneta_swbm_add_rx_fragment(struct mvneta_port *pp,
+			    struct mvneta_rx_desc *rx_desc,
+			    struct mvneta_rx_queue *rxq,
+			    struct page *page)
+{
+	struct net_device *dev = pp->dev;
+	enum dma_data_direction dma_dir;
+	int data_len, len;
+
+	if (rxq->left_size > MVNETA_MAX_RX_BUF_SIZE) {
+		len = MVNETA_MAX_RX_BUF_SIZE;
+		data_len = len;
+	} else {
+		len = rxq->left_size;
+		data_len = len - ETH_FCS_LEN;
+	}
+	dma_dir = page_pool_get_dma_dir(rxq->page_pool);
+	dma_sync_single_for_cpu(dev->dev.parent,
+				rx_desc->buf_phys_addr,
+				len, dma_dir);
+	if (data_len > 0) {
+		/* refill descriptor with new buffer later */
+		skb_add_rx_frag(rxq->skb,
+				skb_shinfo(rxq->skb)->nr_frags,
+				page, NET_SKB_PAD, data_len,
+				PAGE_SIZE);
+	}
+	page_pool_release_page(rxq->page_pool, page);
+	rx_desc->buf_phys_addr = 0;
+	rxq->left_size -= len;
+}
+
 /* Main rx processing when using software buffer management */
 static int mvneta_rx_swbm(struct napi_struct *napi,
 			  struct mvneta_port *pp, int budget,
 			  struct mvneta_rx_queue *rxq)
 {
+	int rcvd_pkts = 0, rcvd_bytes = 0, rx_proc = 0;
 	struct net_device *dev = pp->dev;
-	int rx_todo, rx_proc;
-	int refill = 0;
-	u32 rcvd_pkts = 0;
-	u32 rcvd_bytes = 0;
+	int rx_todo, refill;
 
 	/* Get number of received packets */
 	rx_todo = mvneta_rxq_busy_desc_num_get(pp, rxq);
-	rx_proc = 0;
 
 	/* Fairness NAPI loop */
-	while ((rcvd_pkts < budget) && (rx_proc < rx_todo)) {
+	while (rx_proc < budget && rx_proc < rx_todo) {
 		struct mvneta_rx_desc *rx_desc = mvneta_rxq_next_desc_get(rxq);
+		u32 rx_status, index;
 		unsigned char *data;
 		struct page *page;
-		dma_addr_t phys_addr;
-		u32 rx_status, index;
-		int rx_bytes, skb_size, copy_size;
-		int frag_num, frag_size, frag_offset;
 
 		index = rx_desc - rxq->descs;
 		page = (struct page *)rxq->buf_virt_addr[index];
@@ -1978,12 +2054,13 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 		/* Prefetch header */
 		prefetch(data);
 
-		phys_addr = rx_desc->buf_phys_addr;
 		rx_status = rx_desc->status;
 		rx_proc++;
 		rxq->refill_num++;
 
 		if (rx_status & MVNETA_RXD_FIRST_DESC) {
+			int err;
+
 			/* Check errors only for FIRST descriptor */
 			if (rx_status & MVNETA_RXD_ERR_SUMMARY) {
 				mvneta_rx_error(pp, rx_desc);
@@ -1991,82 +2068,17 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 				/* leave the descriptor untouched */
 				continue;
 			}
-			rx_bytes = rx_desc->data_size -
-				   (ETH_FCS_LEN + MVNETA_MH_SIZE);
 
-			/* Allocate small skb for each new packet */
-			skb_size = max(rx_copybreak, rx_header_size);
-			rxq->skb = netdev_alloc_skb_ip_align(dev, skb_size);
-			if (unlikely(!rxq->skb)) {
-				netdev_err(dev,
-					   "Can't allocate skb on queue %d\n",
-					   rxq->id);
-				dev->stats.rx_dropped++;
-				rxq->skb_alloc_err++;
+			err = mvneta_swbm_rx_frame(pp, rx_desc, rxq, page);
+			if (err)
 				continue;
-			}
-			copy_size = min(skb_size, rx_bytes);
-
-			/* Copy data from buffer to SKB, skip Marvell header */
-			memcpy(rxq->skb->data, data + MVNETA_MH_SIZE,
-			       copy_size);
-			skb_put(rxq->skb, copy_size);
-			rxq->left_size = rx_bytes - copy_size;
-
-			mvneta_rx_csum(pp, rx_status, rxq->skb);
-			if (rxq->left_size == 0) {
-				int size = copy_size + MVNETA_MH_SIZE;
-
-				dma_sync_single_range_for_cpu(dev->dev.parent,
-							      phys_addr, 0,
-							      size,
-							      DMA_FROM_DEVICE);
-
-				/* leave the descriptor and buffer untouched */
-			} else {
-				/* refill descriptor with new buffer later */
-				rx_desc->buf_phys_addr = 0;
-
-				frag_num = 0;
-				frag_offset = copy_size + MVNETA_MH_SIZE;
-				frag_size = min(rxq->left_size,
-						(int)(PAGE_SIZE - frag_offset));
-				skb_add_rx_frag(rxq->skb, frag_num, page,
-						frag_offset, frag_size,
-						PAGE_SIZE);
-				page_pool_release_page(rxq->page_pool, page);
-				rxq->left_size -= frag_size;
-			}
 		} else {
-			/* Middle or Last descriptor */
 			if (unlikely(!rxq->skb)) {
 				pr_debug("no skb for rx_status 0x%x\n",
 					 rx_status);
 				continue;
 			}
-			if (!rxq->left_size) {
-				/* last descriptor has only FCS */
-				/* and can be discarded */
-				dma_sync_single_range_for_cpu(dev->dev.parent,
-							      phys_addr, 0,
-							      ETH_FCS_LEN,
-							      DMA_FROM_DEVICE);
-				/* leave the descriptor and buffer untouched */
-			} else {
-				/* refill descriptor with new buffer later */
-				rx_desc->buf_phys_addr = 0;
-
-				frag_num = skb_shinfo(rxq->skb)->nr_frags;
-				frag_offset = 0;
-				frag_size = min(rxq->left_size,
-						(int)(PAGE_SIZE - frag_offset));
-				skb_add_rx_frag(rxq->skb, frag_num, page,
-						frag_offset, frag_size,
-						PAGE_SIZE);
-
-				page_pool_release_page(rxq->page_pool, page);
-				rxq->left_size -= frag_size;
-			}
+			mvneta_swbm_add_rx_fragment(pp, rx_desc, rxq, page);
 		} /* Middle or Last descriptor */
 
 		if (!(rx_status & MVNETA_RXD_LAST_DESC))
@@ -2091,7 +2103,6 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 
 		/* clean uncomplete skb pointer in queue */
 		rxq->skb = NULL;
-		rxq->left_size = 0;
 	}
 
 	if (rcvd_pkts)
@@ -2954,7 +2965,7 @@ static void mvneta_rxq_hw_init(struct mvneta_port *pp,
 		/* Set Offset */
 		mvneta_rxq_offset_set(pp, rxq, 0);
 		mvneta_rxq_buf_size_set(pp, rxq, PAGE_SIZE < SZ_64K ?
-					PAGE_SIZE :
+					MVNETA_MAX_RX_BUF_SIZE :
 					MVNETA_RX_BUF_SIZE(pp->pkt_size));
 		mvneta_rxq_bm_disable(pp, rxq);
 		mvneta_rxq_fill(pp, rxq, rxq->size);
@@ -4664,7 +4675,7 @@ static int mvneta_probe(struct platform_device *pdev)
 	SET_NETDEV_DEV(dev, &pdev->dev);
 
 	pp->id = global_port_id++;
-	pp->rx_offset_correction = 0; /* not relevant for SW BM */
+	pp->rx_offset_correction = NET_SKB_PAD;
 
 	/* Obtain access to BM resources if enabled and already initialized */
 	bm_node = of_parse_phandle(dn, "buffer-manager", 0);