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To:     Jason Gunthorpe <jgg@nvidia.com>
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Subject: RE: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for
 domain_alloc_user op
Thread-Topic: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for
 domain_alloc_user op
Thread-Index: AQHZ7GCQqMA2D6hFIkG8of68DC8uNLAlMOeAgABMNICAAR3BAIAGE8WQgACl0QCAAI/EwA==
Date:   Wed, 27 Sep 2023 01:08:01 +0000
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> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, September 27, 2023 12:29 AM
>=20
> On Tue, Sep 26, 2023 at 06:37:55AM +0000, Tian, Kevin wrote:
> > > From: Robin Murphy <robin.murphy@arm.com>
> > > Sent: Friday, September 22, 2023 5:48 PM
> > >
> > > I could go on enjoying myself, but basically yeah, "default" can't be=
 a
> > > type in itself (at best it would be a meta-type which could be
> > > requested, such that it resolves to some real type to actually
> > > allocate), so a good name should reflect what the type functionally
> > > *means* to the user. IIUC the important distinction is that it's an
> > > abstract kernel-owned pagetable for the user to indirectly control vi=
a
> > > the API, rather than one it owns and writes directly (and thus has to=
 be
> > > in a specific agreed format).
> > >
> >
> > IOMMU_HWPT_TYPE_KERNEL then?
> >
> > IOMMU_HWPT_TYPE_GENERIC also doesn't sound a straight word.
>=20
> At the end of the day this enum is the type tag for:
>=20
>  struct iommu_hwpt_alloc {
>  	__u32 size;
>  	__u32 pt_id;
>  	__u32 out_hwpt_id;
>  	__u32 __reserved;
> +	__u32 hwpt_type;
> +	__u32 data_len;
> +	__aligned_u64 data_uptr;
>  };
>=20
> That pointer.
>=20
> IOMMU_HWPT_ALLOC_DATA_NONE =3D 0
> IOMMU_HWPT_ALLOC_DATA_INTEL_VTD
> IOMMU_HWPT_ALLOC_DATA_ARM_SMMUV3
>=20
> etc?
>=20
> DATA_NONE requires data_len =3D=3D 0
>=20

Looks good. Probably hwpt_type can be also renamed to data_type
to better match this interpretation.