From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [PATCH 10/10] x86, ACPI: default to reboot via ACPI (again)
Date: Wed, 12 Nov 2008 20:14:01 -0800
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In-Reply-To: <1226546613.4006.110.camel@yakui_zhao.sh.intel.com> (Zhao Yakui's
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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>, "H. Peter Anvin" <hpa@zytor.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 <yakui.zhao@intel.com> writes:


> 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).

Looking at the coreboot source.  It is indeed defined for Nvidia, SIS,
AMD and several others.

A lot of boards use:
outb(0x02, 0xcf9);
outb(0x06, 0xcf9);

Instead of just writing a plain 6.   I think at least on some machines
there is a requirement for a low to hight transition.

> 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.

Right.  The only scary question is will a motherboard hang if you write
to 0xcf9.  If we don't know of an example where writing to 0xcf9 will prevent
us from getting to the next reset method then adding a generic 0xcf9 is
safe.

If we are totally paranoid we can build of a whitelist of motherboards
where writing to 0xcf9 works.  By reading and checkup on the chipset
docs, but don't make the mistake of thinking 0xcf9 is an Intel only
thing.

Eric