Date:	Thu, 18 Sep 2008 09:53:21 -0400
From:	Bill Davidsen <davidsen@....com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Pavel Machek <pavel@...e.cz>,
	Andrew Paprocki <andrew@...iboo.com>
Subject:  Re: ACPI "Soft-off" power button only rebooting system, not powering
     off

Simon Farnsworth wrote:
> Stephen Clark wrote:
>> Pavel Machek wrote:
>>> On Wed 2008-09-17 08:33:50, Andrew Paprocki wrote:
>>>> On Wed, Sep 17, 2008 at 6:18 AM, Pavel Machek <pavel@...e.cz> wrote:
>>>>> On Wed 2008-09-17 00:50:03, Andrew Paprocki wrote:
>>>>>> I have an AMD / Award BIOS based system which does not properly shut
>>>>>> off when I hold down the power button for 4 seconds. The BIOS is
>>>>>> configured to have "Soft-off" set to "Delay for 4 seconds" which is
>>>>>> supposed to power the machine off if the button is held that long.
>>>>>>
>>>>>> I first thought this could be a BIOS bug, but this *only* appears to
>>>>>> happen while Linux is running. If the computer is running WinXP, it
>>>>> Well, so the BIOS is broken. 4second hold should power down the
>>>>> machine regardless of the operating system.
>>>> Yes, I agree.. I just find it strange that it works on the BIOS screen
>>>> as well as in GRUB, but as soon as Linux boots, it no longer works.
>>>> Since it works under WinXP, there must be some way to get it to work
>>>> properly from the OS side even it if means working around the bug
>>>> somehow.
>>> Try noapic/nolapic/nosmp etc... and ask your vendor to fix the bios ;-).
>>>
>> Why do you say it is the BIOS when it shuts down properly from the GRUB
>> prompt or from in WINXP?
>>
> Because it's only the BIOS that can cause this behaviour.
> 
> When you push the power button, the BIOS is invoked. If you release
> within 4 seconds, the BIOS sends an ACPI event to the running OS,
> telling it that the power button has been pushed.
> 
> If you hold it down for 4 or more seconds, the BIOS is supposed to shut
> the machine down without the OS knowing what's happening (no ACPI
> events, just a loss of power). From your problem description, the BIOS
> is noticing *something* about the way Linux sets things up, and
> *choosing* to reboot instead of cutting the power.
> 
Such as setting a bit to reboot instead of powering off? There are lots of bits 
down in low memory which one BIOS or another use, so it may be functioning as 
intended. You might look for an additional option to reboot instead of power 
down, a feature I think may have been intended for systems without a hardware 
RESET button.

> GRUB doesn't touch hardware without BIOS help, so is unlikely to change
> the system state in a way that tickles this BIOS bug; similarly, BIOSes
> are tested against current Windows versions by vendors, so they'll have
> hacked it around until it worked there.

This certainly may be a bug (ie. unintended behavior), but it may be a feature 
which Linux is enabling unintentionally. Having to use the power button on a 
Linux system would worry me more than having to press the button a second time 
during reboot.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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