net: stmmac: Do not enable RX FIFO overflow interrupts

The RX FIFO overflows when the system is not able to process all received
packets and they start accumulating (first in the DMA queue in memory,
then in the FIFO). An interrupt is then raised for each overflowing packet
and handled in stmmac_interrupt(). This is counter-productive, since it
brings the system (or more likely, one CPU core) to its knees to process
the FIFO overflow interrupts.

stmmac_interrupt() handles overflow interrupts by writing the rx tail ptr
into the corresponding hardware register (according to the MAC spec, this
has the effect of restarting the MAC DMA). However, without freeing any rx
descriptors, the DMA stops right away, and another overflow interrupt is
raised as the FIFO overflows again. Since the DMA is already restarted at
the end of stmmac_rx_refill() after freeing descriptors, disabling FIFO
overflow interrupts and the corresponding handling code has no side effect,
and eliminates the interrupt storm when the RX FIFO overflows.

Signed-off-by: Yannick Vignon <yannick.vignon@nxp.com>
Link: https://lore.kernel.org/r/20210506143312.20784-1-yannick.vignon@oss.nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 2 insertions, 12 deletions

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index e0b7eebcb512..345b4c6d1fd4 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5587,7 +5587,6 @@ static void stmmac_common_interrupt(struct stmmac_priv *priv)
 	/* To handle GMAC own interrupts */
 	if ((priv->plat->has_gmac) || xmac) {
 		int status = stmmac_host_irq_status(priv, priv->hw, &priv->xstats);
-		int mtl_status;
 
 		if (unlikely(status)) {
 			/* For LPI we need to save the tx status */
@@ -5598,17 +5597,8 @@ static void stmmac_common_interrupt(struct stmmac_priv *priv)
 		}
 
 		for (queue = 0; queue < queues_count; queue++) {
-			struct stmmac_rx_queue *rx_q = &priv->rx_queue[queue];
-
-			mtl_status = stmmac_host_mtl_irq_status(priv, priv->hw,
-								queue);
-			if (mtl_status != -EINVAL)
-				status |= mtl_status;
-
-			if (status & CORE_IRQ_MTL_RX_OVERFLOW)
-				stmmac_set_rx_tail_ptr(priv, priv->ioaddr,
-						       rx_q->rx_tail_addr,
-						       queue);
+			status = stmmac_host_mtl_irq_status(priv, priv->hw,
+							    queue);
 		}
 
 		/* PCS link status */