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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        Jason Gunthorpe <jgg@nvidia.com>,
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        "dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
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CC:     Robin Murphy <robin.murphy@arm.com>, Will Deacon <will@kernel.org>,
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        "Liu, Yi L" <yi.l.liu@intel.com>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        "Zanussi, Tom" <tom.zanussi@intel.com>
Subject: RE: [PATCH v2 3/8] iommu/sva: Support reservation of global SVA
 PASIDs
Thread-Topic: [PATCH v2 3/8] iommu/sva: Support reservation of global SVA
 PASIDs
Thread-Index: AQHZYQJVCeSxcwpxvEqJIzexBCJ0H68Py18w
Date:   Tue, 28 Mar 2023 07:35:43 +0000
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References: <20230327232138.1490712-1-jacob.jun.pan@linux.intel.com>
 <20230327232138.1490712-4-jacob.jun.pan@linux.intel.com>
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> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Tuesday, March 28, 2023 7:22 AM
>=20
> +/**
> + * @brief
> + *	Reserve a PASID from the SVA global number space.
> + *
> + * @param min starting range, inclusive
> + * @param max ending range, inclusive
> + * @return The reserved PASID on success or IOMMU_PASID_INVALID on
> failure.
> + */
> +ioasid_t iommu_sva_reserve_pasid(ioasid_t min, ioasid_t max)
> +{
> +	int ret;
> +
> +	if (!pasid_valid(min) || !pasid_valid(max) ||
> +	    min =3D=3D 0 || max < min)
> +		return IOMMU_PASID_INVALID;
> +
> +	ret =3D ida_alloc_range(&iommu_global_pasid_ida, min, max,
> GFP_KERNEL);
> +	if (ret < 0)
> +		return IOMMU_PASID_INVALID;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_reserve_pasid);
> +

Look at this function. There is no single word about sva except
in the function name.

sva is just one user of global pasids.

when a driver supports sva it has to always use global pasids even
for non-sva usages like dma pasid.

but this doesn't mean that we should build the API around sva.

it's really about global pasids.

let's just call it clearly as iommu_alloc_global_pasid(min, max).

Then we can define a wrapper iommu_reserve_global_pasid(pasid)
as iommu_alloc_global_pasid(pasid, pasid).

for PASID#0 driver calls iommu_reserve_global_pasid(0).

for dma pasid driver calls iommu_alloc_global_pasid() to get a random
one instead of reserving pasid#1.

this would be future proof when the same driver starts to allocate
more pasids for other usages e..g siov.