linux-kernel - Re: [PATCH v2 7/8] iommu: Export iommu_get_dma

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Message-ID: <ZCMTf5RwebmELsoT@nvidia.com>
Date:   Tue, 28 Mar 2023 13:19:11 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        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>
Subject: Re: [PATCH v2 7/8] iommu: Export iommu_get_dma_domain

On Tue, Mar 28, 2023 at 08:48:22AM -0700, Jacob Pan wrote:

> > Agree. The kernel driver managing the device wants to get the current 
> > domain of the device then iommu_get_domain_for_dev() is the right
> > interface. It knows the domain is the dma domain.
> This goes back to v1 then :)
> 
> I thought the comments from v1 is that we don't want to check the domain
> type is DMA domain returned by iommu_get_domain_for_dev()
> 
> If the driver "knows" the domain is dma domain, why can't it use
> iommu_get_dma_domain()? seems paradoxical.

Huh?

The DMA API operates on the current domain of the device, be it
IDENTITY or UNMANAGED.

You have to copy whatever the current domain is to the PASID and you
should definately not check if it is DMA or something.

Jason