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, 16 Feb 2023 11:23:29 +0100
From:   Joerg Roedel <joro@...tes.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, jean-philippe@...aro.org,
        darren@...amperecomputing.com, scott@...amperecomputing.com,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        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 Wed, Feb 15, 2023 at 02:57:26PM -0600, Bjorn Helgaas wrote:
> [+cc Will, Robin, Joerg for arm-smmu-v3 page size question]
> 
> On Sun, Feb 12, 2023 at 08:14:48PM +0200, Leon Romanovsky wrote:
> > On Wed, Feb 08, 2023 at 10:43:21AM -0800, Ganapatrao Kulkarni wrote:
> > > As per PCIe specification(section 10.5), If a VF implements an
> > > ATS capability, its associated PF must implement an ATS capability.
> > > The ATS Capabilities in VFs and their associated PFs are permitted to
> > > be enabled independently.

Well, the spec is one thing, existing hardware the other. Have you
checked the history of the PF-before-VF requirement before making that
change?

It is possible that early PASID-capable hardware actually required
PF-before-VF enablement of ATS.

Regards,

	Joerg