linux-kernel - Re: [PATCH] PCI/ATS: Allow to enable ATS on VFs even if it is not enabled on PF

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Date:   Thu, 23 Feb 2023 15:45:20 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, darren@...amperecomputing.com,
        scott@...amperecomputing.com, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev
Subject: Re: [PATCH] PCI/ATS:  Allow to enable ATS on VFs even if it is not
 enabled on PF

On Tue, Feb 21, 2023 at 09:46:24AM -0600, Bjorn Helgaas wrote:
> It's weird to me that the SMMU is between PCI and memory, but the
> driver seems to insert itself in the middle after PCI enumeration.
> And maybe even after some PCI device driver binding?

No this shouldn't happen, because device drivers expect DMA to be
operational in their probe() function, so at that point the IOMMU must be
configured. The core and IOMMU subsystems enforce probe dependency between
the SMMU and the PCI device, using links described by ACPI or device tree.

Thanks,
Jean