linux-kernel - Re: [PATCH v2 0/8] Enable PASID for DMA API users

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Date:   Tue, 15 Mar 2022 08:49:12 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        "Jason Gunthorpe" <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 0/8] Enable PASID for DMA API users

Hi Kevin,

On Tue, 15 Mar 2022 08:16:59 +0000, "Tian, Kevin" <kevin.tian@...el.com>
wrote:

> > From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Sent: Tuesday, March 15, 2022 1:07 PM
> > 
> > Some modern accelerators such as Intel's Data Streaming Accelerator
> > (DSA) require PASID in DMA requests to be operational. Specifically,
> > the work submissions with ENQCMD on shared work queues require PASIDs.
> > The use cases
> > include both user DMA with shared virtual addressing (SVA) and in-kernel
> > DMA similar to legacy DMA w/o PASID. Here we address the latter.
> > 
> > DMA mapping API is the de facto standard for in-kernel DMA. However, it
> > operates on a per device or Requester ID(RID) basis which is not
> > PASID-aware. To leverage DMA API for devices relies on PASIDs, this
> > patchset introduces the following APIs
> > 
> > 1. A driver facing API that enables DMA API PASID usage:
> > iommu_enable_pasid_dma(struct device *dev, ioasid_t &pasid);  
> 
> Should this be called dma_enable_pasid() since it's about DMA API? Doing
> so also avoids the driver to include iommu.h.
> 
PASID is still tied to IOMMU, drivers who wants to use this must explicitly
put dependency on IOMMU. So I prefer not to give that illusion.

> Thanks
> Kevin


Thanks,

Jacob