[PATCH net-next 1/6] net: bcmgenet: convert RX path to page_pool

[Nicolai Buchwitz <nb@tipi-net.de>]

Replace the per-packet __netdev_alloc_skb() + dma_map_single() in the
RX path with page_pool, which provides efficient page recycling and
DMA mapping management. This is a prerequisite for XDP support (which
requires stable page-backed buffers rather than SKB linear data).

Key changes:
- Create a page_pool per RX ring (PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV)
- bcmgenet_rx_refill() allocates pages via page_pool_alloc_pages()
- bcmgenet_desc_rx() builds SKBs from pages via napi_build_skb() with
  skb_mark_for_recycle() for automatic page_pool return
- Buffer layout reserves XDP_PACKET_HEADROOM (256 bytes) before the HW
  RSB (64 bytes) + alignment pad (2 bytes) for future XDP headroom

Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
---
 drivers/net/ethernet/broadcom/Kconfig         |   1 +
 .../net/ethernet/broadcom/genet/bcmgenet.c    | 210 ++++++++++++------
 .../net/ethernet/broadcom/genet/bcmgenet.h    |   4 +
 3 files changed, 143 insertions(+), 72 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/Kconfig b/drivers/net/ethernet/broadcom/Kconfig
index cd7dddeb91dd..e3b9a5272406 100644
--- a/drivers/net/ethernet/broadcom/Kconfig
+++ b/drivers/net/ethernet/broadcom/Kconfig
@@ -78,6 +78,7 @@ config BCMGENET
 	select BCM7XXX_PHY
 	select MDIO_BCM_UNIMAC
 	select DIMLIB
+	select PAGE_POOL
 	select BROADCOM_PHY if ARCH_BCM2835
 	help
 	  This driver supports the built-in Ethernet MACs found in the
diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index 482a31e7b72b..bf3f881108f8 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -52,6 +52,14 @@
 #define RX_BUF_LENGTH		2048
 #define SKB_ALIGNMENT		32
 
+/* Page pool RX buffer layout:
+ * XDP_PACKET_HEADROOM | RSB(64) + pad(2) | frame data | skb_shared_info
+ * The HW writes the 64B RSB + 2B alignment padding before the frame.
+ */
+#define GENET_XDP_HEADROOM	XDP_PACKET_HEADROOM
+#define GENET_RSB_PAD		(sizeof(struct status_64) + 2)
+#define GENET_RX_HEADROOM	(GENET_XDP_HEADROOM + GENET_RSB_PAD)
+
 /* Tx/Rx DMA register offset, skip 256 descriptors */
 #define WORDS_PER_BD(p)		(p->hw_params->words_per_bd)
 #define DMA_DESC_SIZE		(WORDS_PER_BD(priv) * sizeof(u32))
@@ -1895,21 +1903,13 @@ static struct sk_buff *bcmgenet_free_tx_cb(struct device *dev,
 }
 
 /* Simple helper to free a receive control block's resources */
-static struct sk_buff *bcmgenet_free_rx_cb(struct device *dev,
-					   struct enet_cb *cb)
+static void bcmgenet_free_rx_cb(struct enet_cb *cb,
+				struct page_pool *pool)
 {
-	struct sk_buff *skb;
-
-	skb = cb->skb;
-	cb->skb = NULL;
-
-	if (dma_unmap_addr(cb, dma_addr)) {
-		dma_unmap_single(dev, dma_unmap_addr(cb, dma_addr),
-				 dma_unmap_len(cb, dma_len), DMA_FROM_DEVICE);
-		dma_unmap_addr_set(cb, dma_addr, 0);
+	if (cb->rx_page) {
+		page_pool_put_full_page(pool, cb->rx_page, false);
+		cb->rx_page = NULL;
 	}
-
-	return skb;
 }
 
 /* Unlocked version of the reclaim routine */
@@ -2248,46 +2248,30 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
 	goto out;
 }
 
-static struct sk_buff *bcmgenet_rx_refill(struct bcmgenet_priv *priv,
-					  struct enet_cb *cb)
+static int bcmgenet_rx_refill(struct bcmgenet_rx_ring *ring,
+			      struct enet_cb *cb)
 {
-	struct device *kdev = &priv->pdev->dev;
-	struct sk_buff *skb;
-	struct sk_buff *rx_skb;
+	struct bcmgenet_priv *priv = ring->priv;
 	dma_addr_t mapping;
+	struct page *page;
 
-	/* Allocate a new Rx skb */
-	skb = __netdev_alloc_skb(priv->dev, priv->rx_buf_len + SKB_ALIGNMENT,
-				 GFP_ATOMIC | __GFP_NOWARN);
-	if (!skb) {
+	page = page_pool_alloc_pages(ring->page_pool,
+				     GFP_ATOMIC | __GFP_NOWARN);
+	if (!page) {
 		priv->mib.alloc_rx_buff_failed++;
 		netif_err(priv, rx_err, priv->dev,
-			  "%s: Rx skb allocation failed\n", __func__);
-		return NULL;
-	}
-
-	/* DMA-map the new Rx skb */
-	mapping = dma_map_single(kdev, skb->data, priv->rx_buf_len,
-				 DMA_FROM_DEVICE);
-	if (dma_mapping_error(kdev, mapping)) {
-		priv->mib.rx_dma_failed++;
-		dev_kfree_skb_any(skb);
-		netif_err(priv, rx_err, priv->dev,
-			  "%s: Rx skb DMA mapping failed\n", __func__);
-		return NULL;
+			  "%s: Rx page allocation failed\n", __func__);
+		return -ENOMEM;
 	}
 
-	/* Grab the current Rx skb from the ring and DMA-unmap it */
-	rx_skb = bcmgenet_free_rx_cb(kdev, cb);
+	/* page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
+	mapping = page_pool_get_dma_addr(page) + GENET_XDP_HEADROOM;
 
-	/* Put the new Rx skb on the ring */
-	cb->skb = skb;
-	dma_unmap_addr_set(cb, dma_addr, mapping);
-	dma_unmap_len_set(cb, dma_len, priv->rx_buf_len);
+	cb->rx_page = page;
+	cb->rx_page_offset = GENET_XDP_HEADROOM;
 	dmadesc_set_addr(priv, cb->bd_addr, mapping);
 
-	/* Return the current Rx skb to caller */
-	return rx_skb;
+	return 0;
 }
 
 /* bcmgenet_desc_rx - descriptor based rx process.
@@ -2339,23 +2323,32 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
 	while ((rxpktprocessed < rxpkttoprocess) &&
 	       (rxpktprocessed < budget)) {
 		struct status_64 *status;
+		struct page *rx_page;
+		unsigned int rx_off;
 		__be16 rx_csum;
+		void *hard_start;
 
 		cb = &priv->rx_cbs[ring->read_ptr];
-		skb = bcmgenet_rx_refill(priv, cb);
 
-		if (unlikely(!skb)) {
+		/* Save the received page before refilling */
+		rx_page = cb->rx_page;
+		rx_off = cb->rx_page_offset;
+
+		if (bcmgenet_rx_refill(ring, cb)) {
 			BCMGENET_STATS64_INC(stats, dropped);
 			goto next;
 		}
 
-		status = (struct status_64 *)skb->data;
+		page_pool_dma_sync_for_cpu(ring->page_pool, rx_page, 0,
+					   RX_BUF_LENGTH);
+
+		hard_start = page_address(rx_page) + rx_off;
+		status = (struct status_64 *)hard_start;
 		dma_length_status = status->length_status;
 		if (dev->features & NETIF_F_RXCSUM) {
 			rx_csum = (__force __be16)(status->rx_csum & 0xffff);
 			if (rx_csum) {
-				skb->csum = (__force __wsum)ntohs(rx_csum);
-				skb->ip_summed = CHECKSUM_COMPLETE;
+				/* defer csum setup to after skb is built */
 			}
 		}
 
@@ -2373,7 +2366,8 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
 		if (unlikely(len > RX_BUF_LENGTH)) {
 			netif_err(priv, rx_status, dev, "oversized packet\n");
 			BCMGENET_STATS64_INC(stats, length_errors);
-			dev_kfree_skb_any(skb);
+			page_pool_put_full_page(ring->page_pool, rx_page,
+						true);
 			goto next;
 		}
 
@@ -2381,7 +2375,8 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
 			netif_err(priv, rx_status, dev,
 				  "dropping fragmented packet!\n");
 			BCMGENET_STATS64_INC(stats, fragmented_errors);
-			dev_kfree_skb_any(skb);
+			page_pool_put_full_page(ring->page_pool, rx_page,
+						true);
 			goto next;
 		}
 
@@ -2409,24 +2404,48 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
 						DMA_RX_RXER)) == DMA_RX_RXER)
 				u64_stats_inc(&stats->errors);
 			u64_stats_update_end(&stats->syncp);
-			dev_kfree_skb_any(skb);
+			page_pool_put_full_page(ring->page_pool, rx_page,
+						true);
 			goto next;
 		} /* error packet */
 
-		skb_put(skb, len);
+		/* Build SKB from the page - data starts at hard_start,
+		 * frame begins after RSB(64) + pad(2) = 66 bytes.
+		 */
+		skb = napi_build_skb(hard_start, PAGE_SIZE - GENET_XDP_HEADROOM);
+		if (unlikely(!skb)) {
+			BCMGENET_STATS64_INC(stats, dropped);
+			page_pool_put_full_page(ring->page_pool, rx_page,
+						true);
+			goto next;
+		}
+
+		skb_mark_for_recycle(skb);
 
-		/* remove RSB and hardware 2bytes added for IP alignment */
-		skb_pull(skb, 66);
-		len -= 66;
+		/* Reserve the RSB + pad, then set the data length */
+		skb_reserve(skb, GENET_RSB_PAD);
+		__skb_put(skb, len - GENET_RSB_PAD);
 
 		if (priv->crc_fwd_en) {
-			skb_trim(skb, len - ETH_FCS_LEN);
+			skb_trim(skb, skb->len - ETH_FCS_LEN);
 			len -= ETH_FCS_LEN;
 		}
 
+		/* Set up checksum offload */
+		if (dev->features & NETIF_F_RXCSUM) {
+			rx_csum = (__force __be16)(status->rx_csum & 0xffff);
+			if (rx_csum) {
+				skb->csum = (__force __wsum)ntohs(rx_csum);
+				skb->ip_summed = CHECKSUM_COMPLETE;
+			}
+		}
+
+		len = skb->len;
 		bytes_processed += len;
 
-		/*Finish setting up the received SKB and send it to the kernel*/
+		/* Finish setting up the received SKB and send it to the
+		 * kernel.
+		 */
 		skb->protocol = eth_type_trans(skb, priv->dev);
 
 		u64_stats_update_begin(&stats->syncp);
@@ -2495,12 +2514,11 @@ static void bcmgenet_dim_work(struct work_struct *work)
 	dim->state = DIM_START_MEASURE;
 }
 
-/* Assign skb to RX DMA descriptor. */
+/* Assign page_pool pages to RX DMA descriptors. */
 static int bcmgenet_alloc_rx_buffers(struct bcmgenet_priv *priv,
 				     struct bcmgenet_rx_ring *ring)
 {
 	struct enet_cb *cb;
-	struct sk_buff *skb;
 	int i;
 
 	netif_dbg(priv, hw, priv->dev, "%s\n", __func__);
@@ -2508,10 +2526,7 @@ static int bcmgenet_alloc_rx_buffers(struct bcmgenet_priv *priv,
 	/* loop here for each buffer needing assign */
 	for (i = 0; i < ring->size; i++) {
 		cb = ring->cbs + i;
-		skb = bcmgenet_rx_refill(priv, cb);
-		if (skb)
-			dev_consume_skb_any(skb);
-		if (!cb->skb)
+		if (bcmgenet_rx_refill(ring, cb))
 			return -ENOMEM;
 	}
 
@@ -2520,16 +2535,19 @@ static int bcmgenet_alloc_rx_buffers(struct bcmgenet_priv *priv,
 
 static void bcmgenet_free_rx_buffers(struct bcmgenet_priv *priv)
 {
-	struct sk_buff *skb;
+	struct bcmgenet_rx_ring *ring;
 	struct enet_cb *cb;
-	int i;
-
-	for (i = 0; i < priv->num_rx_bds; i++) {
-		cb = &priv->rx_cbs[i];
+	int q, i;
 
-		skb = bcmgenet_free_rx_cb(&priv->pdev->dev, cb);
-		if (skb)
-			dev_consume_skb_any(skb);
+	for (q = 0; q <= priv->hw_params->rx_queues; q++) {
+		ring = &priv->rx_rings[q == priv->hw_params->rx_queues ?
+				       DESC_INDEX : q];
+		if (!ring->page_pool)
+			continue;
+		for (i = 0; i < ring->size; i++) {
+			cb = ring->cbs + i;
+			bcmgenet_free_rx_cb(cb, ring->page_pool);
+		}
 	}
 }
 
@@ -2747,6 +2765,31 @@ static void bcmgenet_init_tx_ring(struct bcmgenet_priv *priv,
 	netif_napi_add_tx(priv->dev, &ring->napi, bcmgenet_tx_poll);
 }
 
+static int bcmgenet_rx_ring_create_pool(struct bcmgenet_priv *priv,
+					struct bcmgenet_rx_ring *ring)
+{
+	struct page_pool_params pp_params = {
+		.order = 0,
+		.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
+		.pool_size = ring->size,
+		.nid = NUMA_NO_NODE,
+		.dev = &priv->pdev->dev,
+		.dma_dir = DMA_FROM_DEVICE,
+		.offset = GENET_XDP_HEADROOM,
+		.max_len = RX_BUF_LENGTH,
+	};
+
+	ring->page_pool = page_pool_create(&pp_params);
+	if (IS_ERR(ring->page_pool)) {
+		int err = PTR_ERR(ring->page_pool);
+
+		ring->page_pool = NULL;
+		return err;
+	}
+
+	return 0;
+}
+
 /* Initialize a RDMA ring */
 static int bcmgenet_init_rx_ring(struct bcmgenet_priv *priv,
 				 unsigned int index, unsigned int size,
@@ -2765,10 +2808,17 @@ static int bcmgenet_init_rx_ring(struct bcmgenet_priv *priv,
 	ring->cb_ptr = start_ptr;
 	ring->end_ptr = end_ptr - 1;
 
-	ret = bcmgenet_alloc_rx_buffers(priv, ring);
+	ret = bcmgenet_rx_ring_create_pool(priv, ring);
 	if (ret)
 		return ret;
 
+	ret = bcmgenet_alloc_rx_buffers(priv, ring);
+	if (ret) {
+		page_pool_destroy(ring->page_pool);
+		ring->page_pool = NULL;
+		return ret;
+	}
+
 	bcmgenet_init_dim(ring, bcmgenet_dim_work);
 	bcmgenet_init_rx_coalesce(ring);
 
@@ -2961,6 +3011,20 @@ static void bcmgenet_fini_rx_napi(struct bcmgenet_priv *priv)
 	}
 }
 
+static void bcmgenet_destroy_rx_page_pools(struct bcmgenet_priv *priv)
+{
+	struct bcmgenet_rx_ring *ring;
+	unsigned int i;
+
+	for (i = 0; i <= priv->hw_params->rx_queues; ++i) {
+		ring = &priv->rx_rings[i];
+		if (ring->page_pool) {
+			page_pool_destroy(ring->page_pool);
+			ring->page_pool = NULL;
+		}
+	}
+}
+
 /* Initialize Rx queues
  *
  * Queues 0-15 are priority queues. Hardware Filtering Block (HFB) can be
@@ -3032,6 +3096,7 @@ static void bcmgenet_fini_dma(struct bcmgenet_priv *priv)
 	}
 
 	bcmgenet_free_rx_buffers(priv);
+	bcmgenet_destroy_rx_page_pools(priv);
 	kfree(priv->rx_cbs);
 	kfree(priv->tx_cbs);
 }
@@ -3108,6 +3173,7 @@ static int bcmgenet_init_dma(struct bcmgenet_priv *priv, bool flush_rx)
 	if (ret) {
 		netdev_err(priv->dev, "failed to initialize Rx queues\n");
 		bcmgenet_free_rx_buffers(priv);
+		bcmgenet_destroy_rx_page_pools(priv);
 		kfree(priv->rx_cbs);
 		kfree(priv->tx_cbs);
 		return ret;
diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.h b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
index 9e4110c7fdf6..11a0ec563a89 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.h
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
@@ -15,6 +15,7 @@
 #include <linux/phy.h>
 #include <linux/dim.h>
 #include <linux/ethtool.h>
+#include <net/page_pool/helpers.h>
 
 #include "../unimac.h"
 
@@ -469,6 +470,8 @@ struct bcmgenet_rx_stats64 {
 
 struct enet_cb {
 	struct sk_buff      *skb;
+	struct page         *rx_page;
+	unsigned int        rx_page_offset;
 	void __iomem *bd_addr;
 	DEFINE_DMA_UNMAP_ADDR(dma_addr);
 	DEFINE_DMA_UNMAP_LEN(dma_len);
@@ -575,6 +578,7 @@ struct bcmgenet_rx_ring {
 	struct bcmgenet_net_dim dim;
 	u32		rx_max_coalesced_frames;
 	u32		rx_coalesce_usecs;
+	struct page_pool *page_pool;
 	struct bcmgenet_priv *priv;
 };
 
-- 
2.51.0