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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
CC:     "Raj, Ashok" <ashok.raj@intel.com>,
        David Airlie <airlied@linux.ie>,
        "Robin Murphy" <robin.murphy@arm.com>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        "Ben Skeggs" <bskeggs@redhat.com>, Daniel Vetter <daniel@ffwll.ch>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Will Deacon <will@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 7/7] iommu: Add iommu_domain::domain_ops
Thread-Topic: [PATCH 7/7] iommu: Add iommu_domain::domain_ops
Thread-Index: AQHYEPHVdqbh5j+v9U2GKt1N4SJ4Aqxx7UaggAB9gYCAAH5J0A==
Date:   Tue, 25 Jan 2022 00:58:04 +0000
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References: <20220124071103.2097118-1-baolu.lu@linux.intel.com>
 <20220124071103.2097118-8-baolu.lu@linux.intel.com>
 <BN9PR11MB5276BE30652988271878E78C8C5E9@BN9PR11MB5276.namprd11.prod.outlook.com>
 <20220124171759.GD966497@nvidia.com>
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> From: Jason Gunthorpe via iommu
> Sent: Tuesday, January 25, 2022 1:18 AM
>=20
> On Mon, Jan 24, 2022 at 09:58:18AM +0000, Tian, Kevin wrote:
> > > From: Lu Baolu <baolu.lu@linux.intel.com>
> > > Sent: Monday, January 24, 2022 3:11 PM
> > > +/**
> > > + * struct domain_ops - per-domain ops
> > > + * @attach_dev: attach an iommu domain to a device
> > > + * @detach_dev: detach an iommu domain from a device
> >
> > What is the criteria about whether an op should be iommu_ops or
> domain_ops
> > when it requires both domain and device pointers like above two (and
> future
> > PASID-based attach)?
> >
> > Other examples include:
> > 	@apply_resv_region
>=20
> For apply_resv_region the 'dev' argument is really selecting a device
> that is already attached to the domain, so it should be in the domain
> ops.

Looks this one can be just removed. No iommu driver implements today.

>=20
> > 	@is_attach_deferred
>=20
> Only two drivers implement this and neither use the domain
> argument. Remove the domain argument and keep it in the iommu_ops
>=20

Yes, especially when none of the two drivers actually uses domain.

Generally it makes sense to me by putting all attach related callbacks in
iommu_ops, since they are all for building connections between device
and domain while such connection is device specific (just like how a
vfio device is connected to iommufd).

This in concept also applies to @enable_nesting which you mentioned
in another thread. Nesting is a per-device configuration between multiple
domains attached by a same device.

Thanks
Kevin