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

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Message-ID: <aHi5IUXqHJZGB67M@willie-the-truck>
Date: Thu, 17 Jul 2025 09:49:37 +0100
From: Will Deacon <will@...nel.org>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net,
	bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
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Subject: Re: [PATCH v9 23/29] iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type
 and vsmmu_init impl ops

Hi Nicolin,

On Tue, Jul 15, 2025 at 11:42:24AM -0700, Nicolin Chen wrote:
> Sorry for the late response.

No problem at all.

> 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?

Yup.

> 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?

Yes, please.

> > 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.

Thank you!

Will