[PATCH] iommu/arm-smmu-v3: Stop pre-zeroing batch commands in arm_smmu_atc_inv_master()

Pre-zeroing the batched commands structure is inefficient, as individual
commands are zeroed later in arm_smmu_cmdq_build_cmd(). Therefore, only
the member 'num' needs to be initialized to 0.

Signed-off-by: Zhen Lei <redacted>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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 50a9db5bac466c7..e6882ae81fd08f6 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -1776,10 +1776,11 @@ static int arm_smmu_atc_inv_master(struct arm_smmu_master *master)
 {
 	int i;
 	struct arm_smmu_cmdq_ent cmd;
-	struct arm_smmu_cmdq_batch cmds = {};
+	struct arm_smmu_cmdq_batch cmds;
 
 	arm_smmu_atc_inv_to_cmd(0, 0, 0, &cmd);
 
+	cmds.num = 0;
 	for (i = 0; i < master->num_streams; i++) {
 		cmd.atc.sid = master->streams[i].id;
 		arm_smmu_cmdq_batch_add(master->smmu, &cmds, &cmd);

-- 
2.26.0.106.g9fadedd


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On 17/08/2021 12:34, Zhen Lei wrote:

Pre-zeroing the batched commands structure is inefficient, as individual
commands are zeroed later in arm_smmu_cmdq_build_cmd(). Therefore, only
the member 'num' needs to be initialized to 0.

Signed-off-by: Zhen Lei <redacted>

Reviewed-by: John Garry <redacted>

We prob should have added a comment why we do this (and at the other 
sites). I think Robin said something similar in another patch.

  	for (i = 0; i < master->num_streams; i++) {
  		cmd.atc.sid = master->streams[i].id;
  		arm_smmu_cmdq_batch_add(master->smmu, &cmds, &cmd);

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On Tue, 17 Aug 2021 19:34:11 +0800, Zhen Lei wrote:

Pre-zeroing the batched commands structure is inefficient, as individual
commands are zeroed later in arm_smmu_cmdq_build_cmd(). Therefore, only
the member 'num' needs to be initialized to 0.

Applied to will (for-joerg/arm-smmu/updates), thanks!

[1/1] iommu/arm-smmu-v3: Stop pre-zeroing batch commands in arm_smmu_atc_inv_master()
      https://git.kernel.org/will/c/93f9f7958f12

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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