Describe the power management relationship between a tunneled USB3 device
and the tunnel providing USB4 host with a device link as the relationship
between them is not evident from normal device hierarchy.
Tunneling capable ports have an ACPI _DSD object pointing to the USB4
Host Interface that is used to establish USB3 3.x tunnels
Set the link directly between tunneled USB3 devices and USB4 Host
Interface to ensure that the USB4 host can runtime suspend if no tunneled
USB 3.x devices exist.
Current Thunderbolt code sets a link between USB4 Host Interface and USB3
xHCI host which prevents USB4 Host Interface from runtime suspending even
if the USB3 host is only serving native USB devices.
See commit b2be2b05cf ("thunderbolt: Create device links from ACPI
description") for details.
As the device link is only set for USB3 devices that are already tunneled
we know that USB4 Host Interface exists and is bound to its driver.
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240830152630.3943215-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
f1bfb4a6fe