Re: [PATCH v9 23/29] iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type and vsmmu_init impl ops

[Nicolin Chen <nicolinc@nvidia.com>]

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