I have 4 USB controllers onboard my Asus X399A Prime mobo. They are separated into own IOMMU groupings using "pcie_acs_override=downstream,multifunction"
But the sharp eye will see that the last 2 controllers have the same address for stubbing.... Does that mean they have to be treated as one controller?
IOMMU group 15: [1022:43ba] 01:00.0 USB controller: Advanced Micro Devices, Inc. [AMD] X399 Series Chipset USB 3.1 xHCI Controller (rev 02)
IOMMU group 26: [1b21:2142] 09:00.0 USB controller: ASMedia Technology Inc. Device 2142
IOMMU group 34: [1022:145c] 0d:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-0fh) USB 3.0 Host Controller
IOMMU group 53: [1022:145c] 43:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 00h-0fh) USB 3.0 Host Controller