+++ This bug was initially created as a clone of Bug #949981 +++

This one is from upstream. Our experimentation always produced contradictory
results. Upstream tests showed that the issue depends on the type of the
chipset used:

From: Laura Abbott <labbott@fedoraproject.org>

We received several reports of systems rebooting and powering on
after an attempted shutdown. Testing showed that setting
XHCI_SPURIOUS_WAKEUP quirk in addition to the XHCI_SPURIOUS_REBOOT
quirk allowed the system to shutdown as expected for LynxPoint-LP
xHCI controllers. Set the quirk back.

Note that the quirk was originally introduced for LynxPoint and
LynxPoint-LP just for this same reason. See:

commit 638298dc66ea ("xhci: Fix spurious wakeups after S5 on Haswell")

It was later limited to only concern HP machines as it caused
regression on some machines, see both bug and commit:

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=66171
commit 6962d914f317 ("xhci: Limit the spurious wakeup fix only to HP machines")

Later it was discovered that the powering on after shutdown
was limited to LynxPoint-LP (Haswell-ULT) and that some non-LP HP
machine suffered from spontaneous resume from S3 (which should
not be related to the SPURIOUS_WAKEUP quirk at all). An attempt
to fix this then removed the SPURIOUS_WAKEUP flag usage completely.

commit b45abacde3d5 ("xhci: no switching back on non-ULT Haswell")

Current understanding is that LynxPoint-LP (Haswell ULT) machines
need the SPURIOUS_WAKEUP quirk, otherwise they will restart, and
plain Lynxpoint (Haswell) machines may _not_ have the quirk
set otherwise they again will restart.