Subject: [PATCH net-next 3/5] net: stmmac: simplify DMA descriptor allocation/init/freeing

From: "Russell King (Oracle)" <[email-masked]>
Date: Wed, 18 Mar 2026 18:26:44 +0000

Rather than having separate branches to handle the different types of
descriptors, use the helper functions to calculate the total size of
the DMA descriptors.

Use this to allocate or free the descriptor array, and use a local
variable to hold the address of the descriptor array, so we only need
one dma_alloc_coherent() or dma_free_coherent() call in these paths.

Also do the same for the receive ring initialisation. The transmit
ring can't be converted as there is a case where stmmac_mode_init()
is not called.

Signed-off-by: Russell King (Oracle) <[email-masked]>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 57 +++++++++----------
 1 file changed, 27 insertions(+), 30 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 567499e74917..8a84fdd4577d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1885,6 +1885,7 @@ static int __init_dma_rx_desc_rings(struct stmmac_priv *priv,
 				    u32 queue, gfp_t flags)
 {
 	struct stmmac_rx_queue *rx_q = &dma_conf->rx_queue[queue];
+	void *des;
 	int ret;
 
 	netif_dbg(priv, probe, priv->dev,
@@ -1928,13 +1929,12 @@ static int __init_dma_rx_desc_rings(struct stmmac_priv *priv,
 	/* Setup the chained descriptor addresses */
 	if (priv->descriptor_mode == STMMAC_CHAIN_MODE) {
 		if (priv->extend_desc)
-			stmmac_mode_init(priv, rx_q->dma_erx,
-					 rx_q->dma_rx_phy,
-					 dma_conf->dma_rx_size, 1);
+			des = rx_q->dma_erx;
 		else
-			stmmac_mode_init(priv, rx_q->dma_rx,
-					 rx_q->dma_rx_phy,
-					 dma_conf->dma_rx_size, 0);
+			des = rx_q->dma_rx;
+
+		stmmac_mode_init(priv, des, rx_q->dma_rx_phy,
+				 dma_conf->dma_rx_size, priv->extend_desc);
 	}
 
 	return 0;
@@ -2148,6 +2148,8 @@ static void __free_dma_rx_desc_resources(struct stmmac_priv *priv,
 					 u32 queue)
 {
 	struct stmmac_rx_queue *rx_q = &dma_conf->rx_queue[queue];
+	size_t size;
+	void *addr;
 
 	/* Release the DMA RX socket buffers */
 	if (rx_q->xsk_pool)
@@ -2159,14 +2161,14 @@ static void __free_dma_rx_desc_resources(struct stmmac_priv *priv,
 	rx_q->xsk_pool = NULL;
 
 	/* Free DMA regions of consistent memory previously allocated */
-	if (!priv->extend_desc)
-		dma_free_coherent(priv->device, dma_conf->dma_rx_size *
-				  sizeof(struct dma_desc),
-				  rx_q->dma_rx, rx_q->dma_rx_phy);
+	if (priv->extend_desc)
+		addr = rx_q->dma_erx;
 	else
-		dma_free_coherent(priv->device, dma_conf->dma_rx_size *
-				  sizeof(struct dma_extended_desc),
-				  rx_q->dma_erx, rx_q->dma_rx_phy);
+		addr = rx_q->dma_rx;
+
+	size = stmmac_get_rx_desc_size(priv) * dma_conf->dma_rx_size;
+
+	dma_free_coherent(priv->device, size, addr, rx_q->dma_rx_phy);
 
 	if (xdp_rxq_info_is_reg(&rx_q->xdp_rxq))
 		xdp_rxq_info_unreg(&rx_q->xdp_rxq);
@@ -2251,6 +2253,8 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv,
 	struct page_pool_params pp_params = { 0 };
 	unsigned int dma_buf_sz_pad, num_pages;
 	unsigned int napi_id;
+	size_t size;
+	void *addr;
 	int ret;
 
 	dma_buf_sz_pad = stmmac_rx_offset(priv) + dma_conf->dma_buf_sz +
@@ -2286,24 +2290,17 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv,
 	if (!rx_q->buf_pool)
 		return -ENOMEM;
 
-	if (priv->extend_desc) {
-		rx_q->dma_erx = dma_alloc_coherent(priv->device,
-						   dma_conf->dma_rx_size *
-						   sizeof(struct dma_extended_desc),
-						   &rx_q->dma_rx_phy,
-						   GFP_KERNEL);
-		if (!rx_q->dma_erx)
-			return -ENOMEM;
+	size = stmmac_get_rx_desc_size(priv) * dma_conf->dma_rx_size;
 
-	} else {
-		rx_q->dma_rx = dma_alloc_coherent(priv->device,
-						  dma_conf->dma_rx_size *
-						  sizeof(struct dma_desc),
-						  &rx_q->dma_rx_phy,
-						  GFP_KERNEL);
-		if (!rx_q->dma_rx)
-			return -ENOMEM;
-	}
+	addr = dma_alloc_coherent(priv->device, size, &rx_q->dma_rx_phy,
+				  GFP_KERNEL);
+	if (!addr)
+		return -ENOMEM;
+
+	if (priv->extend_desc)
+		rx_q->dma_erx = addr;
+	else
+		rx_q->dma_rx = addr;
 
 	if (stmmac_xdp_is_enabled(priv) &&
 	    test_bit(queue, priv->af_xdp_zc_qps))
-- 
2.47.3