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Groups > linux.kernel > #1670680

[PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed in queue_inc_prod

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This function is protected by spinlock, and the latter will do memory
barrier implicitly. So that we can safely use writel_relaxed. In fact, the
dmb operation will lengthen the time protected by lock, which indirectly
increase the locking confliction in the stress scene.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 drivers/iommu/arm-smmu-v3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 380969a..d2fbee3 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -728,7 +728,7 @@ static void queue_inc_prod(struct arm_smmu_queue *q)
 	u32 prod = (Q_WRP(q, q->prod) | Q_IDX(q, q->prod)) + 1;

 	q->prod = Q_OVF(q, q->prod) | Q_WRP(q, prod) | Q_IDX(q, prod);
-	writel(q->prod, q->prod_reg);
+	writel_relaxed(q->prod, q->prod_reg);
 }

 /*
--
2.5.0

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[PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed in queue_inc_prod Zhen Lei <thunder.leizhen@huawei.com> - 2017-06-20 13:10 +0200
  Re: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed  in queue_inc_prod Robin Murphy <robin.murphy@arm.com> - 2017-06-20 13:40 +0200
    Re: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed  in queue_inc_prod "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> - 2017-06-21 03:30 +0200
      Re: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with  writel_relaxed in queue_inc_prod Will Deacon <will.deacon@arm.com> - 2017-06-21 11:10 +0200
        Re: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed  in queue_inc_prod "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> - 2017-06-26 15:40 +0200
          Re: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed  in queue_inc_prod "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> - 2017-06-26 15:50 +0200

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