linux-kernel - Re: [PATCH rfcv2 1/8] iommu/arm-smmu-v3: Clear cmds->num after arm_smmu_cmdq_batch

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Message-ID: <aMDcdmlyCH2ZALPA@Asurada-Nvidia>
Date: Tue, 9 Sep 2025 19:03:34 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Balbir Singh <balbirs@...dia.com>
CC: <jgg@...dia.com>, <will@...nel.org>, <robin.murphy@....com>,
	<joro@...tes.org>, <jean-philippe@...aro.org>, <miko.lenczewski@....com>,
	<peterz@...radead.org>, <smostafa@...gle.com>, <kevin.tian@...el.com>,
	<praan@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH rfcv2 1/8] iommu/arm-smmu-v3: Clear cmds->num after
 arm_smmu_cmdq_batch_submit

On Wed, Sep 10, 2025 at 08:49:52AM +1000, Balbir Singh wrote:
> On 9/9/25 15:42, Nicolin Chen wrote:
> > On Tue, Sep 09, 2025 at 01:16:11PM +1000, Balbir Singh wrote:
> >> On 9/9/25 09:26, Nicolin Chen wrote:
> >>> None of the callers of arm_smmu_cmdq_batch_submit() cares about the batch
> >>> after a submission. So, it'll be certainly safe to nuke the cmds->num, at
> >>> least upon a successful one. This will ease a bit a wrapper function, for
> >>> the new arm_smmu_invs structure.
> >>>
> >>> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> >>> ---
> >>>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 10 ++++++++--
> >>>  1 file changed, 8 insertions(+), 2 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 2a8b46b948f05..cccf8f52ee0d5 100644
> >>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >>> @@ -974,11 +974,17 @@ static void arm_smmu_cmdq_batch_add(struct arm_smmu_device *smmu,
> >>>  	cmds->num++;
> >>>  }
> >>>  
> >>> +/* Clears cmds->num after a successful submission */
> >>>  static int arm_smmu_cmdq_batch_submit(struct arm_smmu_device *smmu,
> >>>  				      struct arm_smmu_cmdq_batch *cmds)
> >>>  {
> >>
> >> Nit: arm_smmu_cmdq_batch_submit_clear()?
> > 
> > Probably not. There is no particular point in highlighting it in
> > the function name, as there is no use case wanting an uncleared
> > version.
> 
> I did not suggest we need an uncleared version, I suggested the change
> in name to highlight that the function has a side-effect of clearing
> the cmds->num

No caller cares about the "side effect"...

Nicolin