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net: stmmac: xgmac2: disable RBUE in default RX interrupt mask

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Enabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive
and can trigger a MAC interrupt storm under heavy RX pressure. When the
DMA runs out of RX descriptors it fires RBUE continuously until software
refills the ring.

However, RBUE is redundant: the normal RX completion interrupt (RIE)
already triggers NAPI, which processes completed descriptors and refills
the ring, causing the DMA to resume. The RBUE handler itself only sets
handle_rx - the same outcome as RIE.

On Agilex5 under heavy RX pressure, the MAC interrupt (which includes
RBUE) was observed firing 1,821,811,555 times against only 2,618,627
actual RX completions - a ~695x ratio - confirming the severity of the
storm.

RBUE does not provide OOM recovery. If page_pool is exhausted,
stmmac_rx_refill() cannot advance the DMA tail pointer, the DMA stays
suspended, and RBUE fires again on the next NAPI completion - a storm
with no forward progress. This patch trades that storm for a clean
stall with the same RX outcome. Proper OOM recovery is a pre-existing
gap outside the scope of this fix.

Note: as a consequence of disabling RBUE, the rx_buf_unav_irq ethtool
counter will always read 0 on XGMAC2 devices. This behaviour is already
inconsistent across DWMAC core versions.

Remove RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX
to prevent the interrupt storm while keeping normal RX handling intact.

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@altera.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260609121703.9736-1-muhammad.nazim.amirul.nazle.asmade@altera.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Nazim Amirul 2026-06-09 05:17:03 -07:00 committed by Jakub Kicinski
parent 81246a6530
commit d3265c19b3
1 changed files with 2 additions and 2 deletions
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4
drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h
View File

@ -379,9 +379,9 @@
#define XGMAC_RIE BIT(6)
#define XGMAC_TBUE BIT(2)
#define XGMAC_TIE BIT(0)
#define XGMAC_DMA_INT_DEFAULT_EN (XGMAC_NIE | XGMAC_AIE | XGMAC_RBUE | \
#define XGMAC_DMA_INT_DEFAULT_EN (XGMAC_NIE | XGMAC_AIE | \
XGMAC_RIE | XGMAC_TIE)
#define XGMAC_DMA_INT_DEFAULT_RX (XGMAC_RBUE | XGMAC_RIE)
#define XGMAC_DMA_INT_DEFAULT_RX (XGMAC_RIE)
#define XGMAC_DMA_INT_DEFAULT_TX (XGMAC_TIE)
#define XGMAC_DMA_CH_Rx_WATCHDOG(x) (0x0000313c + (0x80 * (x)))
#define XGMAC_RWT GENMASK(7, 0)