Re: [PATCH v2 15/16] PCI: Check ACS DSP/USP redirect bits in pci_enable_pasid()

[Jason Gunthorpe <jgg@nvidia.com>]

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