Comment 32 for bug 1419355

Unloading xhci_hcd on a Haswell machine with the recent kernel should reset the link and set the controller to D3. Thus CAP_PM+4 should show the least two bits 03.

If you shutdown after unloading the module, it's essentially identical with the normal shutdown with the quirk -- i.e. it'll reboot soon. However, you can change to D0 via setpci before doing the shutdown. If the problem persists even with the manual D0 adjustment, it would mean that the root cause is the xhci_reset() call. OTOH, if changing to D0 influences on the shutdown behavior, it means that the D3 power-state is the root cause.