From: Bjorn Helgaas <helgaas@kernel•org>
To: Nicolin Chen <nicolinc@nvidia•com>
Cc: jgg@nvidia•com, will@kernel•org, robin.murphy@arm•com,
joro@8bytes•org, bhelgaas@google•com, praan@google•com,
baolu.lu@linux•intel.com, kevin.tian@intel•com,
miko.lenczewski@arm•com, linux-arm-kernel@lists•infradead.org,
iommu@lists•linux.dev, linux-kernel@vger•kernel.org,
linux-pci@vger•kernel.org, dan.j.williams@intel•com,
jonathan.cameron@huawei•com, vsethi@nvidia•com,
linux-cxl@vger•kernel.org, nirmoyd@nvidia•com
Subject: Re: [PATCH v6 1/3] PCI: Add pci_ats_required() for CXL.cache capable devices
Date: Thu, 21 May 2026 16:31:23 -0500 [thread overview]
Message-ID: <20260521213123.GA186424@bhelgaas> (raw)
In-Reply-To: <ag90FlOaljwa0qqU@Asurada-Nvidia>
On Thu, May 21, 2026 at 02:07:34PM -0700, Nicolin Chen wrote:
> On Thu, May 21, 2026 at 03:57:23PM -0500, Bjorn Helgaas wrote:
> > On Thu, May 21, 2026 at 01:34:20PM -0700, Nicolin Chen wrote:
> > > +bool pci_ats_required(struct pci_dev *pdev)
> > > +{
> > > + if (!pci_ats_supported(pdev))
> > > + return false;
> > > +
> > > + /* A VF inherits its PF's requirement for ATS function */
> > > + if (pdev->is_virtfn)
> > > + pdev = pci_physfn(pdev);
> > > +
> > > + return pci_cxl_ats_required(pdev);
> >
> > I acked this before I saw this sashiko feedback, which looks like a
> > legit issue to me:
> >
> > Will this VF inheritance logic ever be reached?
> >
> > According to the PCIe SR-IOV specification (section 9.3.3.1), VFs do
> > not implement the ATS Extended Capability, which means pdev->ats_cap
> > is always 0 for VFs.
Huh. I wish sashiko would include the spec revision because that sure
looks wrong. In PCIe r7.0, there is no sec 9.3.3.1. In PCIe r6.0,
sec 9.3.3.1 is the SR-IOV Extended Capability, which doesn't mention
ATS. In both, sec 10.5.1 is the ATS Extended Capability and says both
PFs and VFs can implement it.
So I think this is OK as-is:
Acked-by: Bjorn Helgaas <bhelgaas@google•com>
next prev parent reply other threads:[~2026-05-21 21:31 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 20:34 [PATCH v6 0/3] Allow ATS to be always on for certain ATS-capable devices Nicolin Chen
2026-05-21 20:34 ` [PATCH v6 1/3] PCI: Add pci_ats_required() for CXL.cache capable devices Nicolin Chen
2026-05-21 20:57 ` Bjorn Helgaas
2026-05-21 21:07 ` Nicolin Chen
2026-05-21 21:31 ` Bjorn Helgaas [this message]
2026-05-21 21:59 ` Nicolin Chen
2026-05-22 9:19 ` Yi Liu
2026-05-21 20:34 ` [PATCH v6 2/3] PCI: Allow ATS to be always on for pre-CXL devices Nicolin Chen
2026-05-22 9:17 ` Yi Liu
2026-05-21 20:34 ` [PATCH v6 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Nicolin Chen
2026-05-28 15:24 ` Pranjal Shrivastava
2026-05-28 15:29 ` Jason Gunthorpe
2026-05-28 16:32 ` Pranjal Shrivastava
2026-05-28 18:00 ` Jason Gunthorpe
2026-05-28 18:14 ` Pranjal Shrivastava
2026-05-28 18:20 ` Nicolin Chen
2026-05-28 20:04 ` Jason Gunthorpe
2026-05-28 20:39 ` Pranjal Shrivastava
2026-05-28 7:35 ` [PATCH v6 0/3] Allow ATS to be always on for certain ATS-capable devices Jörg Rödel
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