[PATCH 6.18 216/333] net: mana: Ring doorbell at 4 CQ wraparounds

Greg Kroah-Hartman
2026-03-17T17:22:56Z

From: Long Li <longli@microsoft.com>

commit dabffd08545ffa1d7183bc45e387860984025291 upstream.

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>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20260226192833.1050807-1-longli@microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ethernet/microsoft/mana/mana_en.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)

--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -1645,8 +1645,14 @@ static void mana_poll_tx_cq(struct mana_
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((cq->gdma_cq->queue_size /
+ COMP_ENTRY_SIZE) * 4,
+ CQE_POLLING_BUFFER));

if (comp_read < 1)
return;
@@ -2031,7 +2037,14 @@ static void mana_poll_rx_cq(struct mana_
struct mana_rxq *rxq = cq->rxq;
int comp_read, i;

- comp_read = mana_gd_poll_cq(cq->gdma_cq, comp, CQE_POLLING_BUFFER);
+ /* 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((cq->gdma_cq->queue_size /
+ COMP_ENTRY_SIZE) * 4,
+ CQE_POLLING_BUFFER));
WARN_ON_ONCE(comp_read > CQE_POLLING_BUFFER);

rxq->xdp_flush = false;
@@ -2076,11 +2089,11 @@ static int mana_cq_handler(void *context
mana_gd_ring_cq(gdma_queue, SET_ARM_BIT);
cq->work_done_since_doorbell = 0;
napi_complete_done(&cq->napi, w);
- } else if (cq->work_done_since_doorbell >
- cq->gdma_cq->queue_size / COMP_ENTRY_SIZE * 4) {
+ } else if (cq->work_done_since_doorbell >=
+ (cq->gdma_cq->queue_size / COMP_ENTRY_SIZE) * 4) {
/* MANA hardware requires at least one doorbell ring every 8
* wraparounds of CQ even if there is no need to arm the CQ.
- * This driver rings the doorbell as soon as we have exceeded
+ * This driver rings the doorbell as soon as it has processed
* 4 wraparounds.
*/
mana_gd_ring_cq(gdma_queue, 0);