The new way to describe relationship between tunneled ports and USB4 NHI
(Native Host Interface) is with ACPI _DSD looking like below for a PCIe
downstream port:

    Scope (\_SB.PCI0)
    {
        Device (NHI0) { } // Thunderbolt NHI

        Device (DSB0) // Hotplug downstream port
        {
            Name (_DSD, Package () {
                ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
                Package () {
                    Package () {"usb4-host-interface", \_SB.PCI0.NHI0},
                    ...
                }
            })
        }
    }

This is "documented" in these [1] USB-IF slides and being used on
systems that ship with Windows.

The _DSD can be added to tunneled USB3 and PCIe ports, and is needed to
make sure the USB4 NHI is resumed before any of the tunneled ports so
the protocol tunnels get established properly before the actual port
itself is resumed. Othwerwise the USB/PCI core find the link may not be
established and starts tearing down the device stack.

This parses the ACPI description each time NHI is probed and tries to
find devices that has the property and it references the NHI in
question. For each matching device a device link from that device to the
NHI is created.

Since USB3 ports themselves do not get runtime suspended with the parent
device (hub) we do not add the link from the USB3 port to USB4 NHI but
instead we add the link from the xHCI device. This makes the device link
usable for runtime PM as well.

[1] https://www.usb.org/sites/default/files/D1T2-2%20-%20USB4%20on%20Windows.pdfSigned-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>