Debugging spurious wakeup

[Gianluca Anzolin <gianluca@sottospazio.it>]

Hello,

I have a curious problem with my system: whenever I wake up the PC with a WOL
magic packet and then power it off the systems comes back to life after a
couple of seconds, by itself.

I can reproduce the problem 100% of the times.

I've been having this problems for years. I remember this same issue occurred
also with my previous computer, with a different mainboard. My current system
has an ASUS P8B-WS mb with a Xeon 1275v2 CPU.

I've ruled out in the time many factors: traffic on the net (by disconnecting
the cable), RTC alarms (by disabling them)... long story short: I'm stuck.

While I'm not the only one with this issue (see[1]), some people have reported
mixed success by blacklisting some components (xhci-pci) or by setting
unrelated BIOS options. Unfortunately these workarounds never worked for me.

So I'm here to ask if there is a way to get the source/cause of the last wakeup
by setting some ACPI debug option. This way I could at least pinpoint the
device/interface that caused the spontaneous wakeup and then debug further or
at least disable it.

I've tried to enable the ACPI hardware-related messages with the kernel
arguments: acpi.debug_layer=0x2 acpi.debug_level=0xffffffff

Unfortunately I can't see the information I'm looking for in the resulting
output. Should I enable some other debug_layer? Could anybody point me in the
right direction?

Thank you and best regards,

Gianluca

[1] https://bbs.archlinux.org/viewtopic.php?id=173648