Subject: Re: [PATCH v3 2/3] PCI: Allow ATS to be always on for pre-CXL devices

From: Nirmoy Das <[email-masked]>
Date: Sun, 8 Mar 2026 21:50:33 +0100

On 07.03.26 00:41, Nicolin Chen wrote:
> Some NVIDIA GPU/NIC devices, although don't implement the CXL config space,
> they have many CXL-like properties. Call this kind "pre-CXL".
>
> Similar to CXL.cache capaiblity, these pre-CXL devices also require the ATS
> function even when their RIDs are IOMMU bypassed, i.e. keep ATS "always on"
> v.s. "on demand" when a non-zero PASID line gets enabled in SVA use cases.
>
> Introduce pci_dev_specific_ats_always_on() quirk function to scan a list of
> IDs for these device. Then, include it pci_ats_always_on().
>
> Suggested-by: Jason Gunthorpe <[email-masked]>
> Signed-off-by: Nicolin Chen <[email-masked]>

Tested-by: Nirmoy Das <[email-masked]>

Reviewed-by: Nirmoy Das <[email-masked]>

> ---
>   drivers/pci/pci.h    |  9 +++++++++
>   drivers/pci/ats.c    |  3 ++-
>   drivers/pci/quirks.c | 26 ++++++++++++++++++++++++++
>   3 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 13d998fbacce6..13fa71f965900 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -1150,6 +1150,15 @@ static inline int pci_dev_specific_reset(struct pci_dev *dev, bool probe)
>   }
>   #endif
>   
> +#if defined(CONFIG_PCI_QUIRKS) && defined(CONFIG_PCI_ATS)
> +bool pci_dev_specific_ats_always_on(struct pci_dev *dev);
> +#else
> +static inline bool pci_dev_specific_ats_always_on(struct pci_dev *dev)
> +{
> +	return false;
> +}
> +#endif
> +
>   #if defined(CONFIG_PCI_QUIRKS) && defined(CONFIG_ARM64)
>   int acpi_get_rc_resources(struct device *dev, const char *hid, u16 segment,
>   			  struct resource *res);
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index cf262eb6e6890..e6995b536ad4c 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -243,7 +243,8 @@ bool pci_ats_always_on(struct pci_dev *pdev)
>   	if (pdev->is_virtfn)
>   		pdev = pci_physfn(pdev);
>   
> -	return pci_cxl_ats_always_on(pdev);
> +	return pci_cxl_ats_always_on(pdev) ||
> +	       pci_dev_specific_ats_always_on(pdev);
>   }
>   EXPORT_SYMBOL_GPL(pci_ats_always_on);
>   
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 48946cca4be72..21451e62f284e 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -5714,6 +5714,32 @@ DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x1457, quirk_intel_e2000_no_ats);
>   DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x1459, quirk_intel_e2000_no_ats);
>   DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x145a, quirk_intel_e2000_no_ats);
>   DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x145c, quirk_intel_e2000_no_ats);
> +
> +static const struct pci_dev_ats_always_on {
> +	u16 vendor;
> +	u16 device;
> +} pci_dev_ats_always_on[] = {
> +	/* NVIDIA GPUs */
> +	{ PCI_VENDOR_ID_NVIDIA, 0x2e12, },
> +	{ PCI_VENDOR_ID_NVIDIA, 0x2e2a, },
> +	{ PCI_VENDOR_ID_NVIDIA, 0x2e2b, },
> +	/* NVIDIA CX10 Family NVlink-C2C */
> +	{ PCI_VENDOR_ID_MELLANOX, 0x2101, },
> +	{ 0 }
> +};
> +
> +/* Some pre-CXL devices require ATS on the RID when it is IOMMU-bypassed */
> +bool pci_dev_specific_ats_always_on(struct pci_dev *pdev)
> +{
> +	const struct pci_dev_ats_always_on *i;
> +
> +	for (i = pci_dev_ats_always_on; i->vendor; i++) {
> +		if (i->vendor == pdev->vendor && i->device == pdev->device)
> +			return true;
> +	}
> +
> +	return false;
> +}
>   #endif /* CONFIG_PCI_ATS */
>   
>   /* Freescale PCIe doesn't support MSI in RC mode */