netdev - [PATCH net-next] amd-xgbe: schedule NAPI on Rx Buffer Unavailable to prevent RX stalls

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Message-ID: <20251124101111.1268731-1-Raju.Rangoju@amd.com>
Date: Mon, 24 Nov 2025 15:41:11 +0530
From: Raju Rangoju <Raju.Rangoju@....com>
To: <netdev@...r.kernel.org>
CC: <pabeni@...hat.com>, <kuba@...nel.org>, <edumazet@...gle.com>,
	<davem@...emloft.net>, <andrew+netdev@...n.ch>, <Shyam-sundar.S-k@....com>,
	Raju Rangoju <Raju.Rangoju@....com>
Subject: [PATCH net-next] amd-xgbe: schedule NAPI on Rx Buffer Unavailable to prevent RX stalls

When Rx Buffer Unavailable (RBU) interrupt is asserted, the device can
stall under load and suffer prolonged receive starvation if polling is
not initiated. Treat RBU as a wakeup source and schedule the appropriate
NAPI instance (per-channel or global) to promptly recover from buffer
shortages and refill descriptors.

Signed-off-by: Raju Rangoju <Raju.Rangoju@....com>
---
 drivers/net/ethernet/amd/xgbe/xgbe-drv.c | 73 +++++++++++++++++-------
 1 file changed, 53 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
index 0653e69f0ef7..ec030198b710 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
@@ -367,10 +367,11 @@ static irqreturn_t xgbe_ecc_isr(int irq, void *data)
 static void xgbe_isr_bh_work(struct work_struct *work)
 {
 	struct xgbe_prv_data *pdata = from_work(pdata, work, dev_bh_work);
+	unsigned int mac_isr, mac_tssr, mac_mdioisr;
 	struct xgbe_hw_if *hw_if = &pdata->hw_if;
-	struct xgbe_channel *channel;
+	bool per_ch_irq, ti, ri, rbu, fbe;
 	unsigned int dma_isr, dma_ch_isr;
-	unsigned int mac_isr, mac_tssr, mac_mdioisr;
+	struct xgbe_channel *channel;
 	unsigned int i;
 
 	/* The DMA interrupt status register also reports MAC and MTL
@@ -384,43 +385,75 @@ static void xgbe_isr_bh_work(struct work_struct *work)
 	netif_dbg(pdata, intr, pdata->netdev, "DMA_ISR=%#010x\n", dma_isr);
 
 	for (i = 0; i < pdata->channel_count; i++) {
+		bool schedule_napi = false;
+		struct napi_struct *napi;
+
 		if (!(dma_isr & (1 << i)))
 			continue;
 
 		channel = pdata->channel[i];
 
 		dma_ch_isr = XGMAC_DMA_IOREAD(channel, DMA_CH_SR);
+		/* Precompute flags once */
+		ti  = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, TI);
+		ri  = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RI);
+		rbu = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RBU);
+		fbe = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, FBE);
+
 		netif_dbg(pdata, intr, pdata->netdev, "DMA_CH%u_ISR=%#010x\n",
 			  i, dma_ch_isr);
 
-		/* The TI or RI interrupt bits may still be set even if using
-		 * per channel DMA interrupts. Check to be sure those are not
-		 * enabled before using the private data napi structure.
+		per_ch_irq = pdata->per_channel_irq;
+
+		/*
+		 * Decide which NAPI to use and whether to schedule:
+		 * - When not using per-channel IRQs: schedule on global NAPI
+		 *   if TI or RI are set.
+		 * - RBU should also trigger NAPI (either per-channel or global)
+		 *   to allow refill.
 		 */
-		if (!pdata->per_channel_irq &&
-		    (XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, TI) ||
-		     XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RI))) {
-			if (napi_schedule_prep(&pdata->napi)) {
-				/* Disable Tx and Rx interrupts */
-				xgbe_disable_rx_tx_ints(pdata);
+		if (!per_ch_irq && (ti || ri))
+			schedule_napi = true;
 
-				/* Turn on polling */
-				__napi_schedule(&pdata->napi);
+		if (rbu) {
+			schedule_napi = true;
+			pdata->ext_stats.rx_buffer_unavailable++;
+			netif_dbg(pdata, intr, pdata->netdev,
+				  "RBU on DMA_CH %u, scheduling %s NAPI\n",
+				  i, per_ch_irq ? "per-channel" : "global");
+		}
+
+		napi = per_ch_irq ? &channel->napi : &pdata->napi;
+
+		if (schedule_napi && napi_schedule_prep(napi)) {
+			/* Disable interrupts appropriately before polling */
+			if (per_ch_irq) {
+				if (pdata->channel_irq_mode)
+					xgbe_disable_rx_tx_int(pdata, channel);
+				else
+					disable_irq_nosync(channel->dma_irq);
+			} else {
+				xgbe_disable_rx_tx_ints(pdata);
 			}
+
+			/* Turn on polling */
+			__napi_schedule(napi);
 		} else {
-			/* Don't clear Rx/Tx status if doing per channel DMA
-			 * interrupts, these will be cleared by the ISR for
-			 * per channel DMA interrupts.
+			/*
+			 * Don't clear Rx/Tx status if doing per-channel DMA
+			 * interrupts; those bits will be serviced/cleared by
+			 * the per-channel ISR/NAPI. In non-per-channel mode
+			 * when we're not scheduling NAPI here, ensure we don't
+			 * accidentally clear TI/RI in HW: zero them in the
+			 * local copy so that the eventual write-back does not
+			 * clear TI/RI.
 			 */
 			XGMAC_SET_BITS(dma_ch_isr, DMA_CH_SR, TI, 0);
 			XGMAC_SET_BITS(dma_ch_isr, DMA_CH_SR, RI, 0);
 		}
 
-		if (XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RBU))
-			pdata->ext_stats.rx_buffer_unavailable++;
-
 		/* Restart the device on a Fatal Bus Error */
-		if (XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, FBE))
+		if (fbe)
 			schedule_work(&pdata->restart_work);
 
 		/* Clear interrupt signals */
-- 
2.34.1