linux-kernel - Re: [PATCH RFC 2/8] iommu/arm-smmu-v3: Add and use static helper function arm_smmu_cmdq_issue_cmd_with

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Date:   Wed, 11 Aug 2021 11:31:08 +0100
From:   John Garry <john.garry@...wei.com>
To:     Will Deacon <will@...nel.org>,
        "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
CC:     Robin Murphy <robin.murphy@....com>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 2/8] iommu/arm-smmu-v3: Add and use static helper
 function arm_smmu_cmdq_issue_cmd_with_sync()

>>>> Obviously, inserting as many commands at a time as possible can reduce the
>>>> number of times the mutex contention participates, thereby improving the
>>>> overall performance. At least it reduces the number of calls to function
>>>> arm_smmu_cmdq_issue_cmdlist().
>>>>
>>>> Therefore, function arm_smmu_cmdq_issue_cmd_with_sync() is added to insert
>>>> the 'cmd+sync' commands at a time.
>>>>
>>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>>>> ---
>>>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 33 +++++++++++++--------
>>>>   1 file changed, 21 insertions(+), 12 deletions(-)
>>>>
>>>> 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 2433d3c29b49ff2..a5361153ca1d6a4 100644
>>>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>>> @@ -858,11 +858,25 @@ static int arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
>>>>   	return arm_smmu_cmdq_issue_cmdlist(smmu, cmd, 1, false);
>>>>   }
>>>>   
>>>> -static int arm_smmu_cmdq_issue_sync(struct arm_smmu_device *smmu)
>>>> +static int __maybe_unused arm_smmu_cmdq_issue_sync(struct arm_smmu_device *smmu)
>>>>   {
>>>>   	return arm_smmu_cmdq_issue_cmdlist(smmu, NULL, 0, true);
>>>>   }
>>>>   
>>>> +static int arm_smmu_cmdq_issue_cmd_with_sync(struct arm_smmu_device *smmu,
>>>> +					     struct arm_smmu_cmdq_ent *ent)
>>>> +{
>>>> +	u64 cmd[CMDQ_ENT_DWORDS];
>>>> +
>>>> +	if (arm_smmu_cmdq_build_cmd(cmd, ent)) {
>>>> +		dev_warn(smmu->dev, "ignoring unknown CMDQ opcode 0x%x\n",
>>>> +			 ent->opcode);
>>>> +		return -EINVAL;

Are any of the errors returned from the "issue command" functions 
actually consumed? I couldn't see it on mainline code from a brief browse.

>>>> +	}
>>>> +
>>>> +	return arm_smmu_cmdq_issue_cmdlist(smmu, cmd, 1, true);

Thanks,
John