linux-kernel - [PATCH net-next 10/10] net: ipa: determine replenish doorbell differently

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Date:   Thu,  3 Feb 2022 11:09:27 -0600
From:   Alex Elder <elder@...aro.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     bjorn.andersson@...aro.org, mka@...omium.org, evgreen@...omium.org,
        cpratapa@...eaurora.org, avuyyuru@...eaurora.org,
        jponduru@...eaurora.org, subashab@...eaurora.org, elder@...nel.org,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next 10/10] net: ipa: determine replenish doorbell differently

Rather than tracking the number of receive buffer transactions that
have been submitted without a doorbell, just track the total number
of transactions that have been issued.  Then ring the doorbell when
that number modulo the replenish batch size is 0.

The effect is roughly the same, but the new count is slightly more
interesting, and this approach will someday allow the replenish
batch size to be tuned at runtime.

Signed-off-by: Alex Elder <elder@...aro.org>
---
 drivers/net/ipa/ipa_endpoint.c | 12 ++++++++----
 drivers/net/ipa/ipa_endpoint.h |  4 ++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
index a236edf5bf068..888e94278a84f 100644
--- a/drivers/net/ipa/ipa_endpoint.c
+++ b/drivers/net/ipa/ipa_endpoint.c
@@ -25,7 +25,8 @@
 
 #define atomic_dec_not_zero(v)	atomic_add_unless((v), -1, 0)
 
-#define IPA_REPLENISH_BATCH	16
+/* Hardware is told about receive buffers once a "batch" has been queued */
+#define IPA_REPLENISH_BATCH	16		/* Must be non-zero */
 
 /* The amount of RX buffer space consumed by standard skb overhead */
 #define IPA_RX_BUFFER_OVERHEAD	(PAGE_SIZE - SKB_MAX_ORDER(NET_SKB_PAD, 0))
@@ -1086,14 +1087,15 @@ static void ipa_endpoint_replenish(struct ipa_endpoint *endpoint)
 		return;
 
 	while ((trans = ipa_endpoint_trans_alloc(endpoint, 1))) {
+		bool doorbell;
+
 		if (ipa_endpoint_replenish_one(endpoint, trans))
 			goto try_again_later;
 
-		if (++endpoint->replenish_ready == IPA_REPLENISH_BATCH)
-			endpoint->replenish_ready = 0;
 
 		/* Ring the doorbell if we've got a full batch */
-		gsi_trans_commit(trans, !endpoint->replenish_ready);
+		doorbell = !(++endpoint->replenish_count % IPA_REPLENISH_BATCH);
+		gsi_trans_commit(trans, doorbell);
 	}
 
 	clear_bit(IPA_REPLENISH_ACTIVE, endpoint->replenish_flags);
@@ -1863,6 +1865,8 @@ u32 ipa_endpoint_init(struct ipa *ipa, u32 count,
 	enum ipa_endpoint_name name;
 	u32 filter_map;
 
+	BUILD_BUG_ON(!IPA_REPLENISH_BATCH);
+
 	if (!ipa_endpoint_data_valid(ipa, count, data))
 		return 0;	/* Error */
 
diff --git a/drivers/net/ipa/ipa_endpoint.h b/drivers/net/ipa/ipa_endpoint.h
index 9a37f9387f011..12fd5b16c18eb 100644
--- a/drivers/net/ipa/ipa_endpoint.h
+++ b/drivers/net/ipa/ipa_endpoint.h
@@ -65,7 +65,7 @@ enum ipa_replenish_flag {
  * @evt_ring_id:	GSI event ring used by the endpoint
  * @netdev:		Network device pointer, if endpoint uses one
  * @replenish_flags:	Replenishing state flags
- * @replenish_ready:	Number of replenish transactions without doorbell
+ * @replenish_count:	Total number of replenish transactions committed
  * @replenish_work:	Work item used for repeated replenish failures
  */
 struct ipa_endpoint {
@@ -84,7 +84,7 @@ struct ipa_endpoint {
 
 	/* Receive buffer replenishing for RX endpoints */
 	DECLARE_BITMAP(replenish_flags, IPA_REPLENISH_COUNT);
-	u32 replenish_ready;
+	u64 replenish_count;
 	struct delayed_work replenish_work;		/* global wq */
 };
 
-- 
2.32.0