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Date: Fri, 4 Apr 2014 19:40:29 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Li, Aubrey" <aubrey.li@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [BUG] x86: reboot doesn't reboot
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* H. Peter Anvin <hpa@zytor.com> wrote:

> On April 4, 2014 9:32:58 AM PDT, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
>
> > Windows does ACPI first, so no. And the Dells were broken even 
> > before we moved ACPI up the list.
> 
> That's not what you said a few posts ago.

Exactly, the claim ws:

  "Windows hits the keyboard controller and then tries the ACPI vector."

Which is obviously not the same as 'Windows does ACPI first'.

So the first step _has_ to be to document exactly what Windows does, 
because that's the hardware ABI that we cannot deviate from much. Or 
if we don't know a detail, document the specific uncertainties, don't 
pretend we know it!

The current documented sequence lists 0xcf9, which seems to be a lie:

/*
 * Windows compatible x86 hardware expects the following on reboot:
 *
 * 1) If the FADT has the ACPI reboot register flag set, try it
 * 2) If still alive, write to the keyboard controller
 * 3) If still alive, write to the ACPI reboot register again
 * 4) If still alive, write to the keyboard controller again
 * 5) If still alive, call the EFI runtime service to reboot
 * 6) If still alive, write to the PCI IO port 0xCF9 to reboot
 * 7) If still alive, inform BIOS to do a proper reboot

Thanks,

	Ingo