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

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Date:   Fri, 5 May 2023 08:28:13 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Will Deacon <will@...nel.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        "Ranganathan, Narayan" <narayan.ranganathan@...el.com>
Subject: RE: [PATCH v5 1/7] iommu: Generalize default PCIe requester ID PASID

> From: Jacob Pan <jacob.jun.pan@...ux.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@...el.com>
> wrote:
> 
> > > From: Jacob Pan <jacob.jun.pan@...ux.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.