Subject: [EXTERNAL] Re: [PATCH net] net: mana: Ring doorbell at 4 CQ
wraparounds

On 25/02/2026 18:49, Long Li wrote:

quoted

MANA hardware requires at least one doorbell ring every 8 wraparounds
of the CQ. The driver rings the doorbell as a form of flow control to
inform hardware that CQEs have been consumed.

The NAPI poll functions mana_poll_tx_cq() and mana_poll_rx_cq() can
poll up to CQE_POLLING_BUFFER (512) completions per call. If the CQ
has fewer than 512 entries, a single poll call can process more than
4 wraparounds without ringing the doorbell. The doorbell threshold
check also uses ">" instead of ">=", delaying the ring by one extra
CQE beyond 4 wraparounds. Combined, these issues can cause the driver
to exceed the 8-wraparound hardware limit, leading to missed
completions and stalled queues.

Fix this by capping the number of CQEs polled per call to 4
wraparounds of the CQ in both TX and RX paths. Also change the
doorbell threshold from ">" to ">=" so the doorbell is rung as soon as
4 wraparounds are reached.

Cc: stable@vger.kernel.org
Fixes: 58a63729c957 ("net: mana: Fix doorbell out of order violation
and avoid unnecessary doorbell rings")
Signed-off-by: Long Li <longli@microsoft.com>
---
  drivers/net/ethernet/microsoft/mana/mana_en.c | 23 +++++++++++++++----
  1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c

b/drivers/net/ethernet/microsoft/mana/mana_en.c
index 9919183ad39e..fe667e0d930d 100644

--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c

@@ -1770,8 +1770,14 @@ static void mana_poll_tx_cq(struct mana_cq *cq)
  	ndev = txq->ndev;
  	apc = netdev_priv(ndev);

+	/* Limit CQEs polled to 4 wraparounds of the CQ to ensure the
+	 * doorbell can be rung in time for the hardware's requirement
+	 * of at least one doorbell ring every 8 wraparounds.
+	 */
  	comp_read = mana_gd_poll_cq(cq->gdma_cq, completions,
-				    CQE_POLLING_BUFFER);
+				    min_t(u32, (cq->gdma_cq->queue_size /

no need for min_t, simple min() can be used, queue_size is already u32

Thank you, I'm sending v2.

Long

quoted

+					   COMP_ENTRY_SIZE) * 4,
+					  CQE_POLLING_BUFFER));

  	if (comp_read < 1)
  		return;

@@ -2156,7 +2162,14 @@ static void mana_poll_rx_cq(struct mana_cq *cq)
  	struct mana_rxq *rxq = cq->rxq;
  	int comp_read, i;

-	comp_read = mana_gd_poll_cq(cq->gdma_cq, comp,

CQE_POLLING_BUFFER);

quoted

+	/* Limit CQEs polled to 4 wraparounds of the CQ to ensure the
+	 * doorbell can be rung in time for the hardware's requirement
+	 * of at least one doorbell ring every 8 wraparounds.
+	 */
+	comp_read = mana_gd_poll_cq(cq->gdma_cq, comp,
+				    min_t(u32, (cq->gdma_cq->queue_size /

same here

quoted

+					   COMP_ENTRY_SIZE) * 4,
+					  CQE_POLLING_BUFFER));
  	WARN_ON_ONCE(comp_read > CQE_POLLING_BUFFER);

  	rxq->xdp_flush = false;