linux-kernel - Re: [PATCH v9 23/29] iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type and vsmmu

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Message-ID: <aHahEP0+LKmeA/Tf@Asurada-Nvidia>
Date: Tue, 15 Jul 2025 11:42:24 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Will Deacon <will@...nel.org>
CC: <jgg@...dia.com>, <kevin.tian@...el.com>, <corbet@....net>,
	<bagasdotme@...il.com>, <robin.murphy@....com>, <joro@...tes.org>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<shuah@...nel.org>, <jsnitsel@...hat.com>, <nathan@...nel.org>,
	<peterz@...radead.org>, <yi.l.liu@...el.com>, <mshavit@...gle.com>,
	<praan@...gle.com>, <zhangzekun11@...wei.com>, <iommu@...ts.linux.dev>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>, <patches@...ts.linux.dev>,
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	<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v9 23/29] iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type
 and vsmmu_init impl ops

Hi Will,

Sorry for the late response.

On Fri, Jul 11, 2025 at 05:14:27PM +0100, Will Deacon wrote:
> >  /* MMIO registers */
> >  #define ARM_SMMU_IDR0			0x0
> > @@ -720,6 +721,10 @@ struct arm_smmu_impl_ops {
> >  	int (*init_structures)(struct arm_smmu_device *smmu);
> >  	struct arm_smmu_cmdq *(*get_secondary_cmdq)(
> >  		struct arm_smmu_device *smmu, struct arm_smmu_cmdq_ent *ent);
> > +	const size_t vsmmu_size;
> > +	const enum iommu_viommu_type vsmmu_type;
> > +	int (*vsmmu_init)(struct arm_vsmmu *vsmmu,
> > +			  const struct iommu_user_data *user_data);
> 
> It would be nice to avoid adding data members to the ops structure, if

You mean the "vsmmu_size" and "vsmmu_type" right?

So you want them to be removed, by having two impl_ops:
	size_t get_vsmmu_size(enum iommu_viommu_type vsmmu_type);
	int (*vsmmu_init)(struct arm_vsmmu *vsmmu,
			  const struct iommu_user_data *user_data);

right?

> at all possible. The easiest thing would probably be to add a function
> for getting the vsmmu size and then pushing the two checks against
> 'vsmmu_type' down into the impl_ops callbacks so that:
> 
>   1. If the type is IOMMU_VIOMMU_TYPE_ARM_SMMUV3, we don't bother with
>      the impl_ops at all in arm_vsmmu_init() and arm_smmu_get_viommu_size()

Hmm, I was hoping for an implementation could support the default
IOMMU_VIOMMU_TYPE_ARM_SMMUV3 while having its own viommu_ops or so.
But I think your suggestion is fine since there is no such a use
case at this moment :)

>   2. Otherwise, we pass the type into the impl_ops and they can check it
> 
> Of course, that can be a patch on top of the series as there's no point
> respinning the whole just for this.

Thanks for that! I can draft a patch to send later this week once
the requirements are confirmed.

Nicolin