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

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Message-ID: <20230328102540.6158e642@jacob-builder>
Date:   Tue, 28 Mar 2023 10:25:40 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.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>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 7/8] iommu: Export iommu_get_dma_domain

Hi Jason,

On Tue, 28 Mar 2023 13:19:11 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> 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.
> 
right, the PASID works for IOVA, passthrough. I misunderstood the v1
review comments. I will go back to use iommu_get_domain_for_dev() but w/o
checking domain types.

Thanks all,

Jacob