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From:   John Garry <john.garry@huawei.com>
To:     <will@kernel.org>, <robin.murphy@arm.com>
CC:     <joro@8bytes.org>, <linux-arm-kernel@lists.infradead.org>,
        <iommu@lists.linux-foundation.org>, <linux-kernel@vger.kernel.org>,
        <linuxarm@huawei.com>, John Garry <john.garry@huawei.com>
Subject: [PATCH] iommu/arm-smmu-v3: Remove some unneeded init in arm_smmu_cmdq_issue_cmdlist()
Date:   Tue, 22 Jun 2021 00:36:34 +0800
Message-ID: <1624293394-202509-1-git-send-email-john.garry@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Members of struct "llq" will be zero-inited, apart from member max_n_shift.
But we write llq.val straight after the init, so it was pointless to zero
init those other members. As such, separately init member max_n_shift
only.

In addition, struct "head" is initialised to "llq" only so that member
max_n_shift is set. But that member is never referenced for "head", so
remove any init there.

Removing these initializations is seen as a small performance optimisation,
as this code is (very) hot path.

Signed-off-by: John Garry <john.garry@huawei.com>

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 54b2f27b81d4..8a8ad49bb7fd 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -727,11 +727,11 @@ static int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
 	unsigned long flags;
 	bool owner;
 	struct arm_smmu_cmdq *cmdq = &smmu->cmdq;
-	struct arm_smmu_ll_queue llq = {
-		.max_n_shift = cmdq->q.llq.max_n_shift,
-	}, head = llq;
+	struct arm_smmu_ll_queue llq, head;
 	int ret = 0;
 
+	llq.max_n_shift = cmdq->q.llq.max_n_shift;
+
 	/* 1. Allocate some space in the queue */
 	local_irq_save(flags);
 	llq.val = READ_ONCE(cmdq->q.llq.val);
-- 
2.26.2