linux-kernel - Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user

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Message-ID: <20210928115751.GK964074@nvidia.com>
Date:   Tue, 28 Sep 2021 08:57:51 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
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        "pbonzini@...hat.com" <pbonzini@...hat.com>,
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        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma
 interfaces

On Tue, Sep 28, 2021 at 07:30:41AM +0000, Tian, Kevin wrote:

> > Also, don't call it "hint", there is nothing hinty about this, it has
> > definitive functional impacts.
> 
> possibly dma_mode (too broad?) or dma_usage

You just need a flag to specify if the driver manages DMA ownership
itself, or if it requires the driver core to setup kernel ownership

DMA_OWNER_KERNEL
DMA_OWNER_DRIVER_CONTROLLED

?

There is a bool 'suprress_bind_attrs' already so it could be done like
this:

 bool suppress_bind_attrs:1;

 /* If set the driver must call iommu_XX as the first action in probe() */
 bool suppress_dma_owner:1;

Which is pretty low cost.

Jason