[PATCH v2 0/3] Allow ATS to be always on for certain ATS-capable devices

Nicolin Chen
2026-02-23T22:52:52Z

PCI ATS function is controlled by IOMMU driver calling pci_enable_ats() and
pci_disable_ats() helpers. In general, IOMMU driver only enables ATS, when
a translation channel is enabled on a PASID, typically for an SVA use case.
When a device's RID is IOMMU bypassed and there is no active PASID running
SVA use case, ATS is always disabled.

However, certain PCIe devices require non-PASID ATS on its RID, even if the
RID is IOMMU bypassed. E.g. CXL.cache capability requires ATS to access the
physical memory; some pre-CXL NVIDIA GPUs also require the ATS to be always
on even when their RIDs are IOMMU bypassed.

Provide a helper function to detect CXL.cache capability and scan through a
pre-CXL device ID list.

As the initial use case, call the helper in ARM SMMUv3 driver and adapt the
driver accordingly with a per-device ats_always_on flag.

This is on Github:
https://github.com/nicolinc/iommufd/commits/pci_ats_always_on-v2/

Changelog
v2
* s/non-CXL/pre-CXL
* Rebase on v7.0-rc1
* Update inline comments and commit message
* Add WARN_ON back at !ptr in arm_smmu_clear_cd()
* Add NVIDIA CX10 Family NVlink-C2C to the pre-CXL list
* Do not add boolean parameter to arm_smmu_attach_dev_ste()
v1
https://lore.kernel.org/all/cover.1768624180.git.nicolinc@nvidia.com/

Nicolin Chen (3):
PCI: Allow ATS to be always on for CXL.cache capable devices
PCI: Allow ATS to be always on for pre-CXL devices
iommu/arm-smmu-v3: Allow ATS to be always on

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 1 +
drivers/pci/pci.h | 9 +++
include/linux/pci-ats.h | 3 +
include/uapi/linux/pci_regs.h | 1 +
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 73 ++++++++++++++++++---
drivers/pci/ats.c | 45 +++++++++++++
drivers/pci/quirks.c | 26 ++++++++
7 files changed, 150 insertions(+), 8 deletions(-)

--
2.43.0