[PATCH net-next 0/6] net: stmmac: cleanup stmmac_xmit()

[PATCH net-next 0/6] net: stmmac: cleanup stmmac_xmit()

[Russell King (Oracle)]

This series continues on from part 2 of the descriptor cleanups, making
stmmac_xmit() more readable.

 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 103 +++++++++++-----------
 1 file changed, 52 insertions(+), 51 deletions(-)

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[PATCH net-next 1/6] net: stmmac: move stmmac_xmit() skb head handling

[Russell King (Oracle)]

The skb head buffer handling is delayed in stmmac_xmit() until after
the skb fragments have been populated into the descriptors. The reason
is this code used to set the OWN bit on the first descriptor, which
then allows the TX DMA to process the first and subsequent descriptors.
However, as of commit 579a25a854d4 ("net: stmmac: Initial support for
TBS") this is now separated, but the comments weren't updated.

Move the code populating the first descriptor along side the jumbo code
which also populates the first descriptor. This gives a consistent
location where we populate the descriptor(s) for the SKB head.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 63 +++++++++----------
 1 file changed, 30 insertions(+), 33 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 5062537f79e9..0586ab13cc48 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4770,6 +4770,33 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		entry = stmmac_jumbo_frm(priv, tx_q, skb, csum_insertion);
 		if (unlikely(entry < 0) && (entry != -EINVAL))
 			goto dma_map_err;
+	} else {
+		bool last_segment = (nfrags == 0);
+
+		dma_addr = dma_map_single(priv->device, skb->data,
+					  nopaged_len, DMA_TO_DEVICE);
+		if (dma_mapping_error(priv->device, dma_addr))
+			goto dma_map_err;
+
+		stmmac_set_tx_skb_dma_entry(tx_q, first_entry, dma_addr,
+					    nopaged_len, false);
+
+		stmmac_set_desc_addr(priv, first_desc, dma_addr);
+
+		if (last_segment)
+			stmmac_set_tx_dma_last_segment(tx_q, first_entry);
+
+		if (unlikely((skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
+			     priv->hwts_tx_en)) {
+			/* declare that device is doing timestamping */
+			skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
+			stmmac_enable_tx_timestamp(priv, first_desc);
+		}
+
+		/* Prepare the first descriptor without setting the OWN bit */
+		stmmac_prepare_tx_desc(priv, first_desc, 1, nopaged_len,
+				       csum_insertion, priv->descriptor_mode,
+				       0, last_segment, skb->len);
 	}
 
 	for (i = 0; i < nfrags; i++) {
@@ -4861,39 +4888,6 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (priv->sarc_type)
 		stmmac_set_desc_sarc(priv, first_desc, priv->sarc_type);
 
-	/* Ready to fill the first descriptor and set the OWN bit w/o any
-	 * problems because all the descriptors are actually ready to be
-	 * passed to the DMA engine.
-	 */
-	if (likely(!is_jumbo)) {
-		bool last_segment = (nfrags == 0);
-
-		dma_addr = dma_map_single(priv->device, skb->data,
-					  nopaged_len, DMA_TO_DEVICE);
-		if (dma_mapping_error(priv->device, dma_addr))
-			goto dma_map_err;
-
-		stmmac_set_tx_skb_dma_entry(tx_q, first_entry, dma_addr,
-					    nopaged_len, false);
-
-		stmmac_set_desc_addr(priv, first_desc, dma_addr);
-
-		if (last_segment)
-			stmmac_set_tx_dma_last_segment(tx_q, first_entry);
-
-		if (unlikely((skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
-			     priv->hwts_tx_en)) {
-			/* declare that device is doing timestamping */
-			skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
-			stmmac_enable_tx_timestamp(priv, first_desc);
-		}
-
-		/* Prepare the first descriptor setting the OWN bit too */
-		stmmac_prepare_tx_desc(priv, first_desc, 1, nopaged_len,
-				       csum_insertion, priv->descriptor_mode,
-				       0, last_segment, skb->len);
-	}
-
 	if (tx_q->tbs & STMMAC_TBS_EN) {
 		struct timespec64 ts = ns_to_timespec64(skb->tstamp);
 
@@ -4901,6 +4895,9 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		stmmac_set_desc_tbs(priv, tbs_desc, ts.tv_sec, ts.tv_nsec);
 	}
 
+	/* Set the OWN bit on the first descriptor now that all descriptors
+	 * for this skb are populated.
+	 */
 	stmmac_set_tx_owner(priv, first_desc);
 
 	netdev_tx_sent_queue(netdev_get_tx_queue(dev, queue), skb->len);
-- 
2.47.3

[PATCH net-next 2/6] net: stmmac: move first xmit descriptor SARC and TBS config

[Russell King (Oracle)]

Move the first transmit descriptor's SARC and TBS configuration
alongside the code which populates the first descriptor, which helps
to keep all the code specific to that descriptor together.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 20 +++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 0586ab13cc48..3d94f632fca6 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4799,6 +4799,16 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 				       0, last_segment, skb->len);
 	}
 
+	if (priv->sarc_type)
+		stmmac_set_desc_sarc(priv, first_desc, priv->sarc_type);
+
+	if (tx_q->tbs & STMMAC_TBS_EN) {
+		struct timespec64 ts = ns_to_timespec64(skb->tstamp);
+
+		tbs_desc = &tx_q->dma_entx[first_entry];
+		stmmac_set_desc_tbs(priv, tbs_desc, ts.tv_sec, ts.tv_nsec);
+	}
+
 	for (i = 0; i < nfrags; i++) {
 		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 		unsigned int frag_size = skb_frag_size(frag);
@@ -4885,16 +4895,6 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		u64_stats_inc(&txq_stats->q.tx_set_ic_bit);
 	u64_stats_update_end(&txq_stats->q_syncp);
 
-	if (priv->sarc_type)
-		stmmac_set_desc_sarc(priv, first_desc, priv->sarc_type);
-
-	if (tx_q->tbs & STMMAC_TBS_EN) {
-		struct timespec64 ts = ns_to_timespec64(skb->tstamp);
-
-		tbs_desc = &tx_q->dma_entx[first_entry];
-		stmmac_set_desc_tbs(priv, tbs_desc, ts.tv_sec, ts.tv_nsec);
-	}
-
 	/* Set the OWN bit on the first descriptor now that all descriptors
 	 * for this skb are populated.
 	 */
-- 
2.47.3

[PATCH net-next 3/6] net: stmmac: move stmmac_xmit() first entry index code

[Russell King (Oracle)]

The handling of the first descriptor index/pointer is split around
the checksum handling which makes no sense. Group this code together.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 3d94f632fca6..d5e28ecf9fb4 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4735,10 +4735,6 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* Check if VLAN can be inserted by HW */
 	has_vlan = stmmac_vlan_insert(priv, skb, tx_q);
 
-	entry = tx_q->cur_tx;
-	first_entry = entry;
-	WARN_ON(tx_q->tx_skbuff[first_entry]);
-
 	csum_insertion = (skb->ip_summed == CHECKSUM_PARTIAL);
 	/* DWMAC IPs can be synthesized to support tx coe only for a few tx
 	 * queues. In that case, checksum offloading for those queues that don't
@@ -4755,6 +4751,10 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		csum_insertion = !csum_insertion;
 	}
 
+	entry = tx_q->cur_tx;
+	first_entry = entry;
+	WARN_ON(tx_q->tx_skbuff[first_entry]);
+
 	desc = stmmac_get_tx_desc(priv, tx_q, entry);
 	first_desc = desc;
 
-- 
2.47.3

[PATCH net-next 4/6] net: stmmac: move stmmac_xmit() initial variable init

[Russell King (Oracle)]

Move tx_q, first_tx and txq_stats just before their first use.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index d5e28ecf9fb4..95da2940cc3d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4692,10 +4692,6 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	dma_addr_t dma_addr;
 	u32 sdu_len;
 
-	tx_q = &priv->dma_conf.tx_queue[queue];
-	txq_stats = &priv->xstats.txq_stats[queue];
-	first_tx = tx_q->cur_tx;
-
 	if (priv->tx_path_in_lpi_mode && priv->eee_sw_timer_en)
 		stmmac_stop_sw_lpi(priv);
 
@@ -4732,6 +4728,9 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		return NETDEV_TX_BUSY;
 	}
 
+	tx_q = &priv->dma_conf.tx_queue[queue];
+	first_tx = tx_q->cur_tx;
+
 	/* Check if VLAN can be inserted by HW */
 	has_vlan = stmmac_vlan_insert(priv, skb, tx_q);
 
@@ -4889,6 +4888,7 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		netif_tx_stop_queue(netdev_get_tx_queue(priv->dev, queue));
 	}
 
+	txq_stats = &priv->xstats.txq_stats[queue];
 	u64_stats_update_begin(&txq_stats->q_syncp);
 	u64_stats_add(&txq_stats->q.tx_bytes, skb->len);
 	if (set_ic)
-- 
2.47.3

[PATCH net-next 5/6] net: stmmac: use first_desc for TBS

[Russell King (Oracle)]

Rather than freshly getting a pointer for the TBS descriptor (because
we want to access its enhanced fields) convert the existing first_desc
basic descriptor to a pointer to the enhanced descriptor.

Add a comment explaining why it is safe to convert from the basic
descriptor pointer to the enhanced descriptor pointer.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 95da2940cc3d..a733249c3f9b 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4801,10 +4801,15 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (priv->sarc_type)
 		stmmac_set_desc_sarc(priv, first_desc, priv->sarc_type);
 
+	/* STMMAC_TBS_EN can only be set if SYMMC_TBS_AVAIL has already
+	 * been set, which means the underlying type of the descriptors
+	 * will be struct stmmac_edesc. Therefore, it is safe to convert
+	 * the basic descriptor to the enhanced descriptor here.
+	 */
 	if (tx_q->tbs & STMMAC_TBS_EN) {
 		struct timespec64 ts = ns_to_timespec64(skb->tstamp);
 
-		tbs_desc = &tx_q->dma_entx[first_entry];
+		tbs_desc = dma_desc_to_edesc(first_desc);
 		stmmac_set_desc_tbs(priv, tbs_desc, ts.tv_sec, ts.tv_nsec);
 	}
 
-- 
2.47.3

[PATCH net-next 6/6] net: stmmac: elminate tbs_desc in stmmac_xmit()

[Russell King (Oracle)]

There is no need to have a local variable for tbs_desc, we can do the
conversion when calling stmmac_set_desc_tbs().

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index a733249c3f9b..c01a10e982b5 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4685,7 +4685,6 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	int gso = skb_shinfo(skb)->gso_type;
 	struct stmmac_txq_stats *txq_stats;
 	struct dma_desc *desc, *first_desc;
-	struct dma_edesc *tbs_desc = NULL;
 	struct stmmac_tx_queue *tx_q;
 	int i, csum_insertion = 0;
 	int entry, first_tx;
@@ -4809,8 +4808,8 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (tx_q->tbs & STMMAC_TBS_EN) {
 		struct timespec64 ts = ns_to_timespec64(skb->tstamp);
 
-		tbs_desc = dma_desc_to_edesc(first_desc);
-		stmmac_set_desc_tbs(priv, tbs_desc, ts.tv_sec, ts.tv_nsec);
+		stmmac_set_desc_tbs(priv, dma_desc_to_edesc(first_desc),
+				    ts.tv_sec, ts.tv_nsec);
 	}
 
 	for (i = 0; i < nfrags; i++) {
-- 
2.47.3

Re: [PATCH net-next 0/6] net: stmmac: cleanup stmmac_xmit()

[Maxime Chevallier]

Hi Rusell,

On 20/03/2026 17:46, Russell King (Oracle) wrote:
> This series continues on from part 2 of the descriptor cleanups, making
> stmmac_xmit() more readable.
> 
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 103 +++++++++++-----------
>  1 file changed, 52 insertions(+), 51 deletions(-)
> 

Tested the entire series on Socfpga, no regressions found, and perfs are
the same as before so for the series,

Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime

Re: [PATCH net-next 0/6] net: stmmac: cleanup stmmac_xmit()

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Fri, 20 Mar 2026 16:46:52 +0000 you wrote:
> This series continues on from part 2 of the descriptor cleanups, making
> stmmac_xmit() more readable.
> 
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 103 +++++++++++-----------
>  1 file changed, 52 insertions(+), 51 deletions(-)

Here is the summary with links:
  - [net-next,1/6] net: stmmac: move stmmac_xmit() skb head handling
    https://git.kernel.org/netdev/net-next/c/fcbf106189aa
  - [net-next,2/6] net: stmmac: move first xmit descriptor SARC and TBS config
    https://git.kernel.org/netdev/net-next/c/cafacdc48a74
  - [net-next,3/6] net: stmmac: move stmmac_xmit() first entry index code
    https://git.kernel.org/netdev/net-next/c/7b8683115034
  - [net-next,4/6] net: stmmac: move stmmac_xmit() initial variable init
    https://git.kernel.org/netdev/net-next/c/2e3bfeb1bc0c
  - [net-next,5/6] net: stmmac: use first_desc for TBS
    https://git.kernel.org/netdev/net-next/c/557ccd54ba14
  - [net-next,6/6] net: stmmac: elminate tbs_desc in stmmac_xmit()
    https://git.kernel.org/netdev/net-next/c/cd1f306e2815

You are awesome, thank you!
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