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To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
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Subject: RE: [PATCH v5 1/7] iommu: Generalize default PCIe requester ID PASID
Thread-Topic: [PATCH v5 1/7] iommu: Generalize default PCIe requester ID PASID
Thread-Index: AQHZeTASrtonzxFRJk+i3Dzn6cfwy69Ad3fg
Date:   Fri, 28 Apr 2023 09:38:32 +0000
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> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Friday, April 28, 2023 1:50 AM
>=20
> PCIe Process address space ID (PASID) is used to tag DMA traffic, it
> provides finer grained isolation than requester ID (RID).
>=20
> For each RID, 0 is as a special PASID for the legacy DMA (without
> PASID), thus RID_PASID. This is universal across all architectures,
> therefore warranted to be declared in the common header.
> Noting that VT-d could support none-zero RID_PASID, but currently not
> used.
>=20
> By having a common RID_PASID, we can avoid conflicts between different
> use cases in the generic code. e.g. SVA and DMA API with PASIDs.

You intend it to be generic but in the end only vt-d driver is changed
to use it in this series...

> @@ -190,6 +190,7 @@ enum iommu_dev_features {
>  	IOMMU_DEV_FEAT_IOPF,
>  };
>=20
> +#define IOMMU_DEF_RID_PASID	(0U) /* Reserved for DMA w/o PASID
> */

Is RID a general team on other platform?

Would IOMMU_DEF_NO_PASID serve the purpose better?