Hi Will and Alex, pci_request_acs is called in drivers/iommu/arm-smmu-v3.c to set pci_acs_enable. PCI subsystem tries to enable ACS as below: pci_device_add --> pci_init_capabilities --> pci_enable_acs in ACPI PCI driver. However, ACPI PCI driver will be called before SMMU v3 driver, which will lead pci_enable_acs to return directly as pci_acs_enable is not set before SMMU v3 driver loading. I think this is a bug, what do you think about this problem? Best, Zhou
