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

["H. Peter Anvin" <hpa@zytor.com>]

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