linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Date:   Tue, 15 Jun 2021 20:40:57 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Robin Murphy <robin.murphy@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Gibson <david@...son.dropbear.id.au>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Tue, Jun 15, 2021 at 11:09:37PM +0000, Tian, Kevin wrote:

> which information can you elaborate? This is the area which I'm not
> familiar with thus would appreciate if you can help explain how this
> bus specific information is utilized within the attach function or 
> sometime later.

This is the idea that the device driver needs to specify which bus
specific protocol it uses to issue DMA's when it attaches itself to an
IOASID. For PCI:

- Normal RID DMA
- PASID DMA
- ENQCMD triggered PASID DMA
- ATS/PRI enabled or not

And maybe more. Eg CXL has some other operating modes, I think

The device knows what it is going to do, we need to convey that to the
IOMMU layer so it is prepared properly.

Jason