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 11:33:45 +0100
From:   Will Deacon <will@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>,
        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()

On Wed, Aug 11, 2021 at 11:31:08AM +0100, John Garry wrote:
> > > > > 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.

I don't think so. Can we actually propagate them?

Will