[PATCH net-next] net: stmmac: add XDP multi-buff support for TX side

[Lorenzo Bianconi]

Extend stmmac_xdp_xmit_xdpf() to transmit XDP frames with fragments
(multi-buff). Each buffer, i.e. the frame head and every frag, is mapped
and programmed into a dedicated TX descriptor.

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi at oss.qualcomm.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 123 ++++++++++++++--------
 1 file changed, 80 insertions(+), 43 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index bf9e7e4cb1c3..41ccde6371ec 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5239,77 +5239,114 @@ static unsigned int stmmac_rx_buf2_len(struct stmmac_priv *priv,
 static int stmmac_xdp_xmit_xdpf(struct stmmac_priv *priv, int queue,
 				struct xdp_frame *xdpf, bool dma_map)
 {
-	struct stmmac_txq_stats *txq_stats = &priv->xstats.txq_stats[queue];
+	struct skb_shared_info *sinfo = xdp_get_shared_info_from_frame(xdpf);
 	struct stmmac_tx_queue *tx_q = &priv->dma_conf.tx_queue[queue];
 	bool csum = !priv->plat->tx_queues_cfg[queue].coe_unsupported;
+	unsigned int first_entry = tx_q->cur_tx;
 	unsigned int entry = tx_q->cur_tx;
-	enum stmmac_txbuf_type buf_type;
-	struct dma_desc *tx_desc;
-	dma_addr_t dma_addr;
-	bool set_ic;
+	int i = 0, num_frames = 1;
+	struct dma_desc *desc;
 
-	if (stmmac_tx_avail(priv, queue) < STMMAC_TX_THRESH(priv))
+	if (unlikely(xdp_frame_has_frags(xdpf)))
+		num_frames += sinfo->nr_frags;
+
+	if (stmmac_tx_avail(priv, queue) < num_frames)
 		return STMMAC_XDP_CONSUMED;
 
 	if (priv->est && priv->est->enable &&
 	    priv->est->max_sdu[queue] &&
-	    xdpf->len > priv->est->max_sdu[queue]) {
+	    xdp_get_frame_len(xdpf) > priv->est->max_sdu[queue]) {
 		priv->xstats.max_sdu_txq_drop[queue]++;
 		return STMMAC_XDP_CONSUMED;
 	}
 
-	tx_desc = stmmac_get_tx_desc(priv, tx_q, entry);
-	if (dma_map) {
-		dma_addr = dma_map_single(priv->device, xdpf->data,
-					  xdpf->len, DMA_TO_DEVICE);
-		if (dma_mapping_error(priv->device, dma_addr))
-			return STMMAC_XDP_CONSUMED;
-
-		buf_type = STMMAC_TXBUF_T_XDP_NDO;
-	} else {
-		struct page *page = virt_to_page(xdpf->data);
-
-		dma_addr = page_pool_get_dma_addr(page) + sizeof(*xdpf) +
-			   xdpf->headroom;
-		dma_sync_single_for_device(priv->device, dma_addr,
-					   xdpf->len, DMA_BIDIRECTIONAL);
+	while (true) {
+		skb_frag_t *frag = i ? &sinfo->frags[i - 1] : NULL;
+		int len = frag ? skb_frag_size(frag) : xdpf->len;
+		bool last_frame = i == num_frames - 1;
+		enum stmmac_txbuf_type buf_type;
+		dma_addr_t dma_addr;
 
-		buf_type = STMMAC_TXBUF_T_XDP_TX;
-	}
+		desc = stmmac_get_tx_desc(priv, tx_q, entry);
+		if (dma_map) {
+			if (frag)
+				dma_addr = skb_frag_dma_map(priv->device,
+							    frag, 0, len,
+							    DMA_TO_DEVICE);
+			else
+				dma_addr = dma_map_single(priv->device,
+							  xdpf->data, len,
+							  DMA_TO_DEVICE);
+			if (dma_mapping_error(priv->device, dma_addr))
+				goto error_dma_unmap;
 
-	stmmac_set_tx_dma_entry(tx_q, entry, buf_type, dma_addr, xdpf->len,
-				false);
-	stmmac_set_tx_dma_last_segment(tx_q, entry);
+			buf_type = STMMAC_TXBUF_T_XDP_NDO;
+		} else {
+			struct page *page;
 
-	tx_q->xdpf[entry] = xdpf;
+			page = frag ? skb_frag_page(frag)
+				    : virt_to_page(xdpf->data);
+			dma_addr = page_pool_get_dma_addr(page);
+			if (frag)
+				dma_addr += skb_frag_off(frag);
+			else
+				dma_addr += sizeof(*xdpf) + xdpf->headroom;
+			dma_sync_single_for_device(priv->device, dma_addr,
+						   len, DMA_BIDIRECTIONAL);
+			buf_type = STMMAC_TXBUF_T_XDP_TX;
+		}
 
-	stmmac_set_desc_addr(priv, tx_desc, dma_addr);
+		stmmac_set_tx_dma_entry(tx_q, entry, buf_type, dma_addr, len,
+					dma_map && frag);
+		stmmac_set_desc_addr(priv, desc, dma_addr);
+		stmmac_prepare_tx_desc(priv, desc, !i, len, csum,
+				       priv->descriptor_mode, !!i, last_frame,
+				       xdp_get_frame_len(xdpf));
+		tx_q->xdpf[entry] = last_frame ? xdpf : NULL;
+		if (last_frame) {
+			stmmac_set_tx_dma_last_segment(tx_q, entry);
+			break;
+		}
 
-	stmmac_prepare_tx_desc(priv, tx_desc, 1, xdpf->len,
-			       csum, priv->descriptor_mode, true, true,
-			       xdpf->len);
+		entry = STMMAC_NEXT_ENTRY(entry, priv->dma_conf.dma_tx_size);
+		i++;
+	}
+	tx_q->tx_count_frames += num_frames;
 
-	tx_q->tx_count_frames++;
+	if (!(tx_q->tx_count_frames % priv->tx_coal_frames[queue])) {
+		struct stmmac_txq_stats *txq_stats;
 
-	if (tx_q->tx_count_frames % priv->tx_coal_frames[queue] == 0)
-		set_ic = true;
-	else
-		set_ic = false;
-
-	if (set_ic) {
+		desc = stmmac_get_tx_desc(priv, tx_q, entry);
+		stmmac_set_tx_ic(priv, desc);
 		tx_q->tx_count_frames = 0;
-		stmmac_set_tx_ic(priv, tx_desc);
+
+		txq_stats = &priv->xstats.txq_stats[queue];
 		u64_stats_update_begin(&txq_stats->q_syncp);
 		u64_stats_inc(&txq_stats->q.tx_set_ic_bit);
 		u64_stats_update_end(&txq_stats->q_syncp);
 	}
 
+	/* Set the OWN bit on the first descriptor now that all descriptors
+	 * for this skb are populated.
+	 */
+	desc = stmmac_get_tx_desc(priv, tx_q, first_entry);
+	stmmac_set_tx_owner(priv, desc);
+	tx_q->cur_tx = STMMAC_NEXT_ENTRY(entry, priv->dma_conf.dma_tx_size);
 	stmmac_enable_dma_transmission(priv, priv->ioaddr, queue);
 
-	entry = STMMAC_NEXT_ENTRY(entry, priv->dma_conf.dma_tx_size);
-	tx_q->cur_tx = entry;
-
 	return STMMAC_XDP_TX;
+
+error_dma_unmap:
+	while (first_entry != entry) {
+		desc = stmmac_get_tx_desc(priv, tx_q, first_entry);
+		stmmac_release_tx_desc(priv, desc, priv->descriptor_mode);
+		stmmac_free_tx_buffer(priv, &priv->dma_conf, queue,
+				      first_entry);
+		first_entry = STMMAC_NEXT_ENTRY(first_entry,
+						priv->dma_conf.dma_tx_size);
+	}
+
+	return STMMAC_XDP_CONSUMED;
 }
 
 static int stmmac_xdp_get_tx_queue(struct stmmac_priv *priv,

---
base-commit: 944ae66642b726bd6b25ae71b1e9ff88a0e0bdb0
change-id: 20260922-b4-stmmac-xmit-mb-bb78e0684cf4

Best regards,
-- 
Lorenzo Bianconi <lorenzo.bianconi at oss.qualcomm.com>