--- /dev/null
+From 3f47e67dff1f7266e112c50313d63824f6f17102 Mon Sep 17 00:00:00 2001
+From: Lorenzo Bianconi <lorenzo@kernel.org>
+Date: Thu, 6 Nov 2025 13:53:23 +0100
+Subject: [PATCH] net: airoha: Add the capability to consume out-of-order DMA
+ tx descriptors
+
+EN7581 and AN7583 SoCs are capable of DMA mapping non-linear tx skbs on
+non-consecutive DMA descriptors. This feature is useful when multiple
+flows are queued on the same hw tx queue since it allows to fully utilize
+the available tx DMA descriptors and to avoid the starvation of
+high-priority flow we have in the current codebase due to head-of-line
+blocking introduced by low-priority flows.
+
+Tested-by: Xuegang Lu <xuegang.lu@airoha.com>
+Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
+Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
+Link: https://patch.msgid.link/20251106-airoha-tx-linked-list-v2-1-0706d4a322bd@kernel.org
+Signed-off-by: Jakub Kicinski <kuba@kernel.org>
+---
+ drivers/net/ethernet/airoha/airoha_eth.c | 85 +++++++++++-------------
+ drivers/net/ethernet/airoha/airoha_eth.h | 7 +-
+ 2 files changed, 45 insertions(+), 47 deletions(-)
+
+--- a/drivers/net/ethernet/airoha/airoha_eth.c
++++ b/drivers/net/ethernet/airoha/airoha_eth.c
+@@ -892,19 +892,13 @@ static int airoha_qdma_tx_napi_poll(stru
+
+ dma_unmap_single(eth->dev, e->dma_addr, e->dma_len,
+ DMA_TO_DEVICE);
+- memset(e, 0, sizeof(*e));
++ e->dma_addr = 0;
++ list_add_tail(&e->list, &q->tx_list);
++
+ WRITE_ONCE(desc->msg0, 0);
+ WRITE_ONCE(desc->msg1, 0);
+ q->queued--;
+
+- /* completion ring can report out-of-order indexes if hw QoS
+- * is enabled and packets with different priority are queued
+- * to same DMA ring. Take into account possible out-of-order
+- * reports incrementing DMA ring tail pointer
+- */
+- while (q->tail != q->head && !q->entry[q->tail].dma_addr)
+- q->tail = (q->tail + 1) % q->ndesc;
+-
+ if (skb) {
+ u16 queue = skb_get_queue_mapping(skb);
+ struct netdev_queue *txq;
+@@ -949,6 +943,7 @@ static int airoha_qdma_init_tx_queue(str
+ q->ndesc = size;
+ q->qdma = qdma;
+ q->free_thr = 1 + MAX_SKB_FRAGS;
++ INIT_LIST_HEAD(&q->tx_list);
+
+ q->entry = devm_kzalloc(eth->dev, q->ndesc * sizeof(*q->entry),
+ GFP_KERNEL);
+@@ -961,9 +956,9 @@ static int airoha_qdma_init_tx_queue(str
+ return -ENOMEM;
+
+ for (i = 0; i < q->ndesc; i++) {
+- u32 val;
++ u32 val = FIELD_PREP(QDMA_DESC_DONE_MASK, 1);
+
+- val = FIELD_PREP(QDMA_DESC_DONE_MASK, 1);
++ list_add_tail(&q->entry[i].list, &q->tx_list);
+ WRITE_ONCE(q->desc[i].ctrl, cpu_to_le32(val));
+ }
+
+@@ -973,9 +968,9 @@ static int airoha_qdma_init_tx_queue(str
+
+ airoha_qdma_wr(qdma, REG_TX_RING_BASE(qid), dma_addr);
+ airoha_qdma_rmw(qdma, REG_TX_CPU_IDX(qid), TX_RING_CPU_IDX_MASK,
+- FIELD_PREP(TX_RING_CPU_IDX_MASK, q->head));
++ FIELD_PREP(TX_RING_CPU_IDX_MASK, 0));
+ airoha_qdma_rmw(qdma, REG_TX_DMA_IDX(qid), TX_RING_DMA_IDX_MASK,
+- FIELD_PREP(TX_RING_DMA_IDX_MASK, q->head));
++ FIELD_PREP(TX_RING_DMA_IDX_MASK, 0));
+
+ return 0;
+ }
+@@ -1031,17 +1026,21 @@ static int airoha_qdma_init_tx(struct ai
+ static void airoha_qdma_cleanup_tx_queue(struct airoha_queue *q)
+ {
+ struct airoha_eth *eth = q->qdma->eth;
++ int i;
+
+ spin_lock_bh(&q->lock);
+- while (q->queued) {
+- struct airoha_queue_entry *e = &q->entry[q->tail];
++ for (i = 0; i < q->ndesc; i++) {
++ struct airoha_queue_entry *e = &q->entry[i];
++
++ if (!e->dma_addr)
++ continue;
+
+ dma_unmap_single(eth->dev, e->dma_addr, e->dma_len,
+ DMA_TO_DEVICE);
+ dev_kfree_skb_any(e->skb);
++ e->dma_addr = 0;
+ e->skb = NULL;
+-
+- q->tail = (q->tail + 1) % q->ndesc;
++ list_add_tail(&e->list, &q->tx_list);
+ q->queued--;
+ }
+ spin_unlock_bh(&q->lock);
+@@ -1883,20 +1882,6 @@ static u32 airoha_get_dsa_tag(struct sk_
+ #endif
+ }
+
+-static bool airoha_dev_tx_queue_busy(struct airoha_queue *q, u32 nr_frags)
+-{
+- u32 tail = q->tail <= q->head ? q->tail + q->ndesc : q->tail;
+- u32 index = q->head + nr_frags;
+-
+- /* completion napi can free out-of-order tx descriptors if hw QoS is
+- * enabled and packets with different priorities are queued to the same
+- * DMA ring. Take into account possible out-of-order reports checking
+- * if the tx queue is full using circular buffer head/tail pointers
+- * instead of the number of queued packets.
+- */
+- return index >= tail;
+-}
+-
+ static int airoha_get_fe_port(struct airoha_gdm_port *port)
+ {
+ struct airoha_qdma *qdma = port->qdma;
+@@ -1919,8 +1904,10 @@ static netdev_tx_t airoha_dev_xmit(struc
+ struct airoha_gdm_port *port = netdev_priv(dev);
+ struct airoha_qdma *qdma = port->qdma;
+ u32 nr_frags, tag, msg0, msg1, len;
++ struct airoha_queue_entry *e;
+ struct netdev_queue *txq;
+ struct airoha_queue *q;
++ LIST_HEAD(tx_list);
+ void *data;
+ int i, qid;
+ u16 index;
+@@ -1966,7 +1953,7 @@ static netdev_tx_t airoha_dev_xmit(struc
+ txq = netdev_get_tx_queue(dev, qid);
+ nr_frags = 1 + skb_shinfo(skb)->nr_frags;
+
+- if (airoha_dev_tx_queue_busy(q, nr_frags)) {
++ if (q->queued + nr_frags >= q->ndesc) {
+ /* not enough space in the queue */
+ netif_tx_stop_queue(txq);
+ spin_unlock_bh(&q->lock);
+@@ -1975,11 +1962,13 @@ static netdev_tx_t airoha_dev_xmit(struc
+
+ len = skb_headlen(skb);
+ data = skb->data;
+- index = q->head;
++
++ e = list_first_entry(&q->tx_list, struct airoha_queue_entry,
++ list);
++ index = e - q->entry;
+
+ for (i = 0; i < nr_frags; i++) {
+ struct airoha_qdma_desc *desc = &q->desc[index];
+- struct airoha_queue_entry *e = &q->entry[index];
+ skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ dma_addr_t addr;
+ u32 val;
+@@ -1989,7 +1978,14 @@ static netdev_tx_t airoha_dev_xmit(struc
+ if (unlikely(dma_mapping_error(dev->dev.parent, addr)))
+ goto error_unmap;
+
+- index = (index + 1) % q->ndesc;
++ list_move_tail(&e->list, &tx_list);
++ e->skb = i ? NULL : skb;
++ e->dma_addr = addr;
++ e->dma_len = len;
++
++ e = list_first_entry(&q->tx_list, struct airoha_queue_entry,
++ list);
++ index = e - q->entry;
+
+ val = FIELD_PREP(QDMA_DESC_LEN_MASK, len);
+ if (i < nr_frags - 1)
+@@ -2002,15 +1998,9 @@ static netdev_tx_t airoha_dev_xmit(struc
+ WRITE_ONCE(desc->msg1, cpu_to_le32(msg1));
+ WRITE_ONCE(desc->msg2, cpu_to_le32(0xffff));
+
+- e->skb = i ? NULL : skb;
+- e->dma_addr = addr;
+- e->dma_len = len;
+-
+ data = skb_frag_address(frag);
+ len = skb_frag_size(frag);
+ }
+-
+- q->head = index;
+ q->queued += i;
+
+ skb_tx_timestamp(skb);
+@@ -2019,7 +2009,7 @@ static netdev_tx_t airoha_dev_xmit(struc
+ if (netif_xmit_stopped(txq) || !netdev_xmit_more())
+ airoha_qdma_rmw(qdma, REG_TX_CPU_IDX(qid),
+ TX_RING_CPU_IDX_MASK,
+- FIELD_PREP(TX_RING_CPU_IDX_MASK, q->head));
++ FIELD_PREP(TX_RING_CPU_IDX_MASK, index));
+
+ if (q->ndesc - q->queued < q->free_thr)
+ netif_tx_stop_queue(txq);
+@@ -2029,10 +2019,13 @@ static netdev_tx_t airoha_dev_xmit(struc
+ return NETDEV_TX_OK;
+
+ error_unmap:
+- for (i--; i >= 0; i--) {
+- index = (q->head + i) % q->ndesc;
+- dma_unmap_single(dev->dev.parent, q->entry[index].dma_addr,
+- q->entry[index].dma_len, DMA_TO_DEVICE);
++ while (!list_empty(&tx_list)) {
++ e = list_first_entry(&tx_list, struct airoha_queue_entry,
++ list);
++ dma_unmap_single(dev->dev.parent, e->dma_addr, e->dma_len,
++ DMA_TO_DEVICE);
++ e->dma_addr = 0;
++ list_move_tail(&e->list, &q->tx_list);
+ }
+
+ spin_unlock_bh(&q->lock);
+--- a/drivers/net/ethernet/airoha/airoha_eth.h
++++ b/drivers/net/ethernet/airoha/airoha_eth.h
+@@ -169,7 +169,10 @@ enum trtcm_param {
+ struct airoha_queue_entry {
+ union {
+ void *buf;
+- struct sk_buff *skb;
++ struct {
++ struct list_head list;
++ struct sk_buff *skb;
++ };
+ };
+ dma_addr_t dma_addr;
+ u16 dma_len;
+@@ -193,6 +196,8 @@ struct airoha_queue {
+ struct napi_struct napi;
+ struct page_pool *page_pool;
+ struct sk_buff *skb;
++
++ struct list_head tx_list;
+ };
+
+ struct airoha_tx_irq_queue {
projects / thirdparty / openwrt.git / commitdiff
