On Thu, Jul 17, 2025 at 06:17:11PM -0400, Donald Dutile wrote: > > > On 7/9/25 10:52 AM, Jason Gunthorpe wrote: > > Switches ignore the PASID when routing TLPs. This means the path from the > > PASID issuing end point to the IOMMU must be direct with no possibility > > for another device to claim the addresses. > > > > This is done using ACS flags and pci_enable_pasid() checks for this. > > So a PASID device is a MFD, and it has ACS caps & bits to check? Not a MFD, but the MFD loopback would follow the same rules for routing PASID TLPs. For a MFD none of the switch specific ACS Enhanced flags would make sense: > > PCI_ACS_DSP_MT_RR: Prevents Downstream Port BAR's from claiming upstream > > flowing transactions > > > > PCI_ACS_USP_MT_RR: Prevents Upstream Port BAR's from claiming upstream > > flowing transactions > > > > PCI_ACS_UNCLAIMED_RR: Prevents a hole in the USP bridge window compared > > to all the DSP bridge windows from generating a > > error. Jason
