RE: [PATCH v5 1/7] iommu: Generalize default PCIe requester ID PASID

Tian, Kevin
2023-05-05T08:30:09Z

> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Friday, April 28, 2023 11:56 PM
>
> Hi Kevin,
>
> On Fri, 28 Apr 2023 09:38:32 +0000, "Tian, Kevin" <kevin.tian@intel.com>
> wrote:
>
> > > From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > > Sent: Friday, April 28, 2023 1:50 AM
> > >
> > > PCIe Process address space ID (PASID) is used to tag DMA traffic, it
> > > provides finer grained isolation than requester ID (RID).
> > >
> > > 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.
> > >
> > > 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...
> change for SVA is in the patch.

My point was that since it is common why there is no change in arm-smmu
driver to use the common macro?

>
> > > @@ -190,6 +190,7 @@ enum iommu_dev_features {
> > > IOMMU_DEV_FEAT_IOPF,
> > > };
> > >
> > > +#define IOMMU_DEF_RID_PASID (0U) /* Reserved for DMA w/o PASID
> > > */
> >
> > Is RID a general team on other platform?
> RID, aka requester id is a PCI term. so I this it is common though on SMMU
> might be better called stream ID PASID?
>
> > Would IOMMU_DEF_NO_PASID serve the purpose better?
> not sure, it is still a PASID. For completeness, might be called
> IOMMU_DEF_PASID_FOR_DMA_NO_PASID :)
>
> other suggestions?
>

that is even worse. Let's keep the original one and see whether others
have better suggestion.