Subject: [PATCH net] net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings

From: [email-masked]
Date: Mon, 5 Aug 2024 16:38:08 -0700

From: Long Li <[email-masked]>

After napi_complete_done() is called, another NAPI may be running on
another CPU and ring the doorbell before the current CPU does. When
combined with unnecessary rings when there is no need to ARM the CQ, this
triggers error paths in the hardware.

Fix this by always ring the doorbell in sequence and avoid unnecessary
rings.

Cc: [email-masked]
Fixes: e1b5683ff62e ("net: mana: Move NAPI from EQ to CQ")
Signed-off-by: Long Li <[email-masked]>
---
 drivers/net/ethernet/microsoft/mana/mana_en.c | 24 ++++++++++++-------
 include/net/mana/mana.h                       |  1 +
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index d2f07e179e86..7d08e23c6749 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -1788,7 +1788,6 @@ static void mana_poll_rx_cq(struct mana_cq *cq)
 static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
 {
 	struct mana_cq *cq = context;
-	u8 arm_bit;
 	int w;
 
 	WARN_ON_ONCE(cq->gdma_cq != gdma_queue);
@@ -1799,16 +1798,23 @@ static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
 		mana_poll_tx_cq(cq);
 
 	w = cq->work_done;
-
-	if (w < cq->budget &&
-	    napi_complete_done(&cq->napi, w)) {
-		arm_bit = SET_ARM_BIT;
-	} else {
-		arm_bit = 0;
+	cq->work_done_since_doorbell += w;
+
+	if (w < cq->budget) {
+		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) {
+		/* MANA hardware requires at least one doorbell ring every 8
+		 * wraparounds of CQ even there is no need to ARM. This driver
+		 * rings the doorbell as soon as we have execceded 4
+		 * wraparounds.
+		 */
+		mana_gd_ring_cq(gdma_queue, 0);
+		cq->work_done_since_doorbell = 0;
 	}
 
-	mana_gd_ring_cq(gdma_queue, arm_bit);
-
 	return w;
 }
 
diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index 6439fd8b437b..7caa334f4888 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -275,6 +275,7 @@ struct mana_cq {
 	/* NAPI data */
 	struct napi_struct napi;
 	int work_done;
+	int work_done_since_doorbell;
 	int budget;
 };
 
-- 
2.17.1