linux-kernel - [PATCH] iommu/arm-smmu-v3: Poll for CMDQ drain completion more effectively

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Date:   Thu, 27 Apr 2017 16:43:07 +0530
From:   sunil.kovvuri@...il.com
To:     will.deacon@....com, robin.murphy@....com,
        iommu@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        robert.richter@...ium.com, jcm@...hat.com,
        Sunil Goutham <sgoutham@...ium.com>, Geetha <gakula@...ium.com>
Subject: [PATCH] iommu/arm-smmu-v3: Poll for CMDQ drain completion more effectively

From: Sunil Goutham <sgoutham@...ium.com>

Modified polling on CMDQ consumer similar to how polling is done for TLB SYNC
completion in SMMUv2 driver. Code changes are done with reference to

8513c8930069 iommu/arm-smmu: Poll for TLB sync completion more effectively

Poll timeout has been increased which addresses issue of 100us timeout not
sufficient, when command queue is full with TLB invalidation commands.

Signed-off-by: Sunil Goutham <sgoutham@...ium.com>
Signed-off-by: Geetha <gakula@...ium.com>
---
 drivers/iommu/arm-smmu-v3.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index d412bdd..34599d4 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -379,6 +379,9 @@
 #define CMDQ_SYNC_0_CS_NONE		(0UL << CMDQ_SYNC_0_CS_SHIFT)
 #define CMDQ_SYNC_0_CS_SEV		(2UL << CMDQ_SYNC_0_CS_SHIFT)
 
+#define CMDQ_DRAIN_TIMEOUT_US		1000
+#define CMDQ_SPIN_COUNT			10
+
 /* Event queue */
 #define EVTQ_ENT_DWORDS			4
 #define EVTQ_MAX_SZ_SHIFT		7
@@ -737,7 +740,8 @@ static void queue_inc_prod(struct arm_smmu_queue *q)
  */
 static int queue_poll_cons(struct arm_smmu_queue *q, bool drain, bool wfe)
 {
-	ktime_t timeout = ktime_add_us(ktime_get(), ARM_SMMU_POLL_TIMEOUT_US);
+	ktime_t timeout = ktime_add_us(ktime_get(), CMDQ_DRAIN_TIMEOUT_US);
+	unsigned int spin_cnt, delay = 1;
 
 	while (queue_sync_cons(q), (drain ? !queue_empty(q) : queue_full(q))) {
 		if (ktime_compare(ktime_get(), timeout) > 0)
@@ -746,8 +750,13 @@ static int queue_poll_cons(struct arm_smmu_queue *q, bool drain, bool wfe)
 		if (wfe) {
 			wfe();
 		} else {
-			cpu_relax();
-			udelay(1);
+			for (spin_cnt = 0;
+			     spin_cnt < CMDQ_SPIN_COUNT; spin_cnt++) {
+				cpu_relax();
+				continue;
+			}
+			udelay(delay);
+			delay *= 2;
 		}
 	}
 
-- 
2.7.4