[PATCH net-next v2] net: stmmac: Avoid freeing and re-requesting IRQ during XDP set prog

Currently stmmac will run a full cycle of IRQ tear down and setup when
setting up a new XDP program. This makes tuning TSN systems difficult
because whenever a new XDP program is installed then the irq threads will
be stopped and restarted which will undo any thread tuning.

The problem is avoided by removing stmmac_free_irq()/stmmac_request_irq()
from stmmac_xdp_release()/stmmac_xdp_open().

stmmac_free_irq() implicitly synchronizes interrupts and, with that
removed, nothing else disabled interrupts or makes later actions in
stmmac_xdp_release() safe when there are concurrent interrupts. Thus the
in addition to removing the code to free the IRQ we must:

 * disable DMA interrupts and explicitly sync the handlers in
   stmmac_xdp_release()
 * remove the code that (needlessly) reinits each channel to
   avoid the DMA interrupts being re-enabled (and which is
   safe because the content of priv->dma_cfg does not change
   due to XDP activity).

Signed-off-by: Daniel Thompson <[email protected]>
---
This patch was developed (and tested) as part of the TC956x work that
Alex Elder and I have been working on. However the change should work with
any driver that uses the stmmac core so it it fully independant of that
work.
---
Changes in v2:
- Added net-next prefix
- Remove stmmac_init_chan() from stmmac_xdp_open() because it will re-enable
  interrupts
- Link to v1: https://lore.kernel.org/r/20260706-tc956x-stmmac-no_irq_teardown-v1-1-df009d0272bf@riscstar.com
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 64 +++++++++++++++++------
 1 file changed, 47 insertions(+), 17 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 2a0d7eff88d3ff1ffa57e224c25f9e77bc28ed10..3cf436014686ad2b65aa69a8fecea97379532576 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2531,6 +2531,23 @@ static void stmmac_enable_all_dma_irq(struct stmmac_priv *priv)
 	}
 }
 
+static void stmmac_disable_all_dma_irq(struct stmmac_priv *priv)
+{
+	u8 rx_channels_count = priv->plat->rx_queues_to_use;
+	u8 tx_channels_count = priv->plat->tx_queues_to_use;
+	u8 dma_csr_ch = max(rx_channels_count, tx_channels_count);
+	u8 chan;
+
+	for (chan = 0; chan < dma_csr_ch; chan++) {
+		struct stmmac_channel *ch = &priv->channel[chan];
+		unsigned long flags;
+
+		spin_lock_irqsave(&ch->lock, flags);
+		stmmac_disable_dma_irq(priv, priv->ioaddr, chan, 1, 1);
+		spin_unlock_irqrestore(&ch->lock, flags);
+	}
+}
+
 /**
  * stmmac_start_all_dma - start all RX and TX DMA channels
  * @priv: driver private structure
@@ -3814,6 +3831,33 @@ static void stmmac_free_irq(struct net_device *dev,
 	}
 }
 
+static void stmmac_synchronize_irq(struct net_device *dev)
+{
+	struct stmmac_priv *priv = netdev_priv(dev);
+	struct stmmac_msi *msi = priv->msi;
+	int j;
+
+	for (j = priv->plat->tx_queues_to_use - 1; msi && j >= 0; j--) {
+		if (msi->tx_irq[j] > 0)
+			synchronize_irq(msi->tx_irq[j]);
+	}
+
+	for (j = priv->plat->rx_queues_to_use - 1; msi && j >= 0; j--) {
+		if (msi->rx_irq[j] > 0)
+			synchronize_irq(msi->rx_irq[j]);
+	}
+
+	if (msi && msi->sfty_ue_irq > 0 && msi->sfty_ue_irq != dev->irq)
+		synchronize_irq(msi->sfty_ue_irq);
+	if (msi && msi->sfty_ce_irq > 0 && msi->sfty_ce_irq != dev->irq)
+		synchronize_irq(msi->sfty_ce_irq);
+	if (priv->wol_irq > 0 && priv->wol_irq != dev->irq)
+		synchronize_irq(priv->wol_irq);
+	if (priv->sfty_irq > 0 && priv->sfty_irq != dev->irq)
+		synchronize_irq(priv->sfty_irq);
+	synchronize_irq(dev->irq);
+}
+
 static int stmmac_msi_init(struct stmmac_priv *priv,
 			   struct stmmac_resources *res)
 {
@@ -7108,8 +7152,9 @@ void stmmac_xdp_release(struct net_device *dev)
 	for (chan = 0; chan < priv->plat->tx_queues_to_use; chan++)
 		hrtimer_cancel(&priv->dma_conf.tx_queue[chan].txtimer);
 
-	/* Free the IRQ lines */
-	stmmac_free_irq(dev, REQ_IRQ_ERR_ALL, 0);
+	/* Silence DMA interrupts */
+	stmmac_disable_all_dma_irq(priv);
+	stmmac_synchronize_irq(dev);
 
 	/* Stop TX/RX DMA channels */
 	stmmac_stop_all_dma(priv);
@@ -7132,7 +7177,6 @@ int stmmac_xdp_open(struct net_device *dev)
 	struct stmmac_priv *priv = netdev_priv(dev);
 	u8 rx_cnt = priv->plat->rx_queues_to_use;
 	u8 tx_cnt = priv->plat->tx_queues_to_use;
-	u8 dma_csr_ch = max(rx_cnt, tx_cnt);
 	struct stmmac_rx_queue *rx_q;
 	struct stmmac_tx_queue *tx_q;
 	bool sph_en;
@@ -7155,12 +7199,6 @@ int stmmac_xdp_open(struct net_device *dev)
 
 	stmmac_reset_queues_param(priv);
 
-	/* DMA CSR Channel configuration */
-	for (chan = 0; chan < dma_csr_ch; chan++) {
-		stmmac_init_chan(priv, priv->ioaddr, priv->plat->dma_cfg, chan);
-		stmmac_disable_dma_irq(priv, priv->ioaddr, chan, 1, 1);
-	}
-
 	/* Adjust Split header */
 	sph_en = (priv->hw->rx_csum > 0) && priv->sph_active;
 
@@ -7197,10 +7235,6 @@ int stmmac_xdp_open(struct net_device *dev)
 	/* Start Rx & Tx DMA Channels */
 	stmmac_start_all_dma(priv);
 
-	ret = stmmac_request_irq(dev);
-	if (ret)
-		goto irq_error;
-
 	/* Enable NAPI process*/
 	stmmac_enable_all_queues(priv);
 	netif_carrier_on(dev);
@@ -7209,10 +7243,6 @@ int stmmac_xdp_open(struct net_device *dev)
 
 	return 0;
 
-irq_error:
-	for (chan = 0; chan < priv->plat->tx_queues_to_use; chan++)
-		hrtimer_cancel(&priv->dma_conf.tx_queue[chan].txtimer);
-
 init_error:
 	free_dma_desc_resources(priv, &priv->dma_conf);
 dma_desc_error:

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260706-tc956x-stmmac-no_irq_teardown-8a7592b9f8c1

Best regards,
-- 
Daniel Thompson <[email protected]>