From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 10/10] x86, ACPI: default to reboot via ACPI (again)
Date: Wed, 12 Nov 2008 19:18:02 -0800
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To: Zhao Yakui <yakui.zhao@intel.com>
Cc: Avi Kivity <avi@redhat.com>, Ingo Molnar <mingo@elte.hu>, Len Brown <lenb@kernel.org>, Stephen Rothwell <sfr@canb.auug.org.au>, Andrew Morton <akpm@linux-foundation.org>, Matthew Garrett <mjg@redhat.com>, "Eric W. Biederman" <ebiederm@xmission.com>, Andrey Borzenkov <arvidjaar@mail.ru>, "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>, "Brown, Len" <len.brown@intel.com>, Thomas Gleixner <tglx@linutronix.de>, Eduardo Habkost <ehabkost@redhat.com>

Zhao Yakui wrote:
> 
> Peter Anvin suggests that OS attempt reboot via 0xCF9 port if avaiable.
> This is not very good. 0xCF9 I/O port is the reset control register
> defined in Intel ICH6/7/8/9 chipset. In theory it is effective for Intel
> chipset. Maybe it is not applied for other chipset(For example: Nvidia,
> ALI, VIA). There exists a laptop in bug 11942, in which the 0xCF9 I/O
> port is defined as the RESET_REG. But unfortunately it can't be rebooted
> Via 0xCF9 I/O port. 
>     In fact although the 0xCF9 is defined for Intel ICH chipset, it
> doesn't mean that all the box based on ICH chipset can be rebooted via
> 0xCF9 I/O port. For example: we have a laptop based on intel ICH6
> chipset that can't be rebooted by writing the 0x06 to 0xCF9 I/O port.
> 

Port CF9 isn't universal, but other vendors are increasingly
implementing it -- I know ALi are in their more recent chipsets.  Either
way, I agree that we need to figure out how to get ACPI to work, but CF9
is a low risk fallback before going to the KBC.

	-hpa