linux-kernel - Re: [PATCH] reboot: perform warm/cold reset correctly for CF9 type

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Message-ID: <52261DC8.4070307@zytor.com>
Date:	Tue, 03 Sep 2013 10:35:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Li, Fei" <fei.li@...el.com>
CC:	Ingo Molnar <mingo@...nel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Liu, Chuansheng" <chuansheng.liu@...el.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"holt@....com" <holt@....com>,
	"rmk+kernel@....linux.org.uk" <rmk+kernel@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] reboot: perform warm/cold reset correctly for CF9 type

On 08/21/2013 08:32 PM, Li, Fei wrote:
> 
> In fact, ACPI method also implements reset by writing RESET_VALUE into RESET_REG
> port. In our platform, it also uses port 0xCF9. The difference between cold and wart reset
> is whether power cycle is involved or not. After all, this is another topic.
> 
> From the source code, CF9 boot method are still used by some apple MAC and dell
> platforms if I understand correctly.
> 
> Back to our patch, if you really concern the effect of cold reboot 0x0E to current existed
> platforms, we can set the default value of reboot_mode as REBOOT_WARM.
> 
> Does it make sense?
> 

Sort-of-kind-of.

The problem here is that "cold" versus "warm" reboot seems to have
slightly different meanings for BIOS (bypass POST) and the CF9 register
(where I presume it is a "deeper" platform reset of some kind ... is it
even well-defined what the semantics are?)

I could be wrong and the cold/warm reset values in CF9 end up having
exactly the same function as the magic BIOS signature does; if so, then
I would like to be told so explicitly, ideally with an explanation about
how it works on the hw level (or a pointer to relevant documentation,
Intel internal docs are fine.)

Finally, again, does this solve a real problem?

	-hpa


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