linux-kernel - Re: [PATCH v3 1/1] PCI: Add translated request only flag for pci_enable

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Message-ID: <Y9gQxCmzqq6WXZK4@nvidia.com>
Date:   Mon, 30 Jan 2023 14:47:32 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Joerg Roedel <jroedel@...e.de>,
        Matt Fagnani <matt.fagnani@...l.net>,
        Christian König <christian.koenig@....com>,
        Kevin Tian <kevin.tian@...el.com>,
        Vasant Hegde <vasant.hegde@....com>,
        Tony Zhu <tony.zhu@...el.com>, linux-pci@...r.kernel.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] PCI: Add translated request only flag for
 pci_enable_pasid()

On Mon, Jan 30, 2023 at 12:38:10PM -0600, Bjorn Helgaas wrote:

> Sorry, I'm still confused.  PCI_PASID_XLATED_REQ_ONLY is a
> device-specific property, and you want to opt-in AMD graphics devices.
> Where's the AMD graphics-specific change?  The current patch does
> this:
> 
>   pdev_pri_ats_enable
>     pci_enable_pasid(pdev, 0, PCI_PASID_XLATED_REQ_ONLY)
> 
> which looks like it does it for *all* devices below an AMD IOMMU,
> without any device or driver input.

AMD GPU has a private interface to AMD IOMMU to support PASID support
that only it uses.

When AMD's IOMMU driver is cleaned up to use the common PASID API this
will have to be moved into the GPU driver.

But we are not there yet..

Jason