Re: Debugging spurious wakeup

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 06/23/2015 08:36 AM, Gianluca Anzolin wrote:
> Hello,
>
> Yesterday I took the time to read the document about GPE / PME handling and I
> compared the wakeup code of my BIOS with the examples in that document.
>
> I noticed that some vital wakeup code was executed only when a variable (PMSX)
> was set. That variable was set by a global NPME() method and that method was
> called by _OSC().
>
> And in my logs I had this message:
>
> giu 19 18:31:06 zanac kernel: acpi PNP0A08:00: _OSC: OS supports
> [ExtendedConfig ASPM ClockPM Segments MSI]
> giu 19 18:31:06 zanac kernel: \_SB_.PCI0:_OSC invalid UUID
> giu 19 18:31:06 zanac kernel: _OSC request data:1 1f 0
> giu 19 18:31:06 zanac kernel: acpi PNP0A08:00: _OSC failed (AE_ERROR);
> disabling ASPM
>
> A googled a bit and found the following bugzilla entry, that applies to my
> situation perfectly: the NEXP variable isn't set anywhere, yet in Windows it
> is.
>
> https://bugzilla.kernel.org/show_bug.cgi?id=36932
>
> So I disassembled the DSDT, I removed any test involving the NEXP variable in
> the code, I recompiled and replaced the table with GRUB.
>
> And then the _OSC() invocation completed successfully, giving me a working WOL
> without spontaneous wakeups!

Great work and thanks for sharing you results !

> What puzzles me is that the location of the NEXP variables is marked as ACPI
> NVS and the kernel never touches that region of memory. What is Windows doing
> differently that makes it work?

Perhaps it is not Windows itself but the motherboard driver fixing a 
known bug ?

   -- Daniel

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