RELENG_6 power button ignored after halt if ACPI enabled

[Mark Kirkwood]

Nate Lawson wrote:

> 
> He isn't doing halt -p, he's doing "halt", then hitting the power 
> button.  If acpi is still enabled, it intercepts the button event but 
> can't do anything because the OS is halted (i.e. no shutdown() 
> available).  If ACPI is disabled by that point, the BIOS handles it and 
> powers off the system.
> 
> This only applies to his system, it's not necessarily true in general. 
> Some systems won't work if ACPI is disabled during this process, hence 
> the sysctl.
> 

What was interesting is that this happened on two reasonably different 
systems:

- Tualatin mobo, VIA chipset, AWARD bios
- Tualatin mobo, Serverworks chipset, AMIBIOS bios

leading me to suspect that there was more general impact for this issue. 
   Given that there has not exactly been a tidal wave of mails to that 
effect :-), I guess it may only apply to circa 2002 Tualatin (or perhaps 
only Supermicro Tualatin) boards. Of course, the other possibility is 
that it *is* more general, but most folks are using 'shutdown -p' and 
are not noticing that the power button does not work....

Cheers

Mark