Hi Matt,

-----Original Message-----
From: Matt Fleming [mailto:matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org]
Sent: Wednesday, March 09, 2016 11:35 PM
To: Chen, Yu C
Cc: Rafael J. Wysocki; Rafael J. Wysocki; ACPI Devel Maling List;
x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org; linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Linux Kernel Mailing List; linux-
pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Len Brown; Thomas Gleixner; Ingo Molnar; H. Peter
Anvin; Zhang, Rui
Subject: Re: [PATCH][RFC v3] ACPI / PM: Fix poweroff issue on HW-full
platforms without _S5

On Tue, 08 Mar, at 04:25:30PM, Chen, Yu C wrote:

quoted

Hum. unfortunately it is not guaranteed to run after all of the other
code, because other components who register pm_power_off may be

built as modules, and

quoted

we can not predict/control the sequence registration.   So this patch may
break the EFI platforms who use non-efi poweroff due to unstable EFI
service ,  not sure if there are any released-products of this kind.

Certainly the majority of x86 client machines do not use EFI power off,
because it hardly ever functions correctly.

quoted

Currently I'm thinking of 3 possible solutions,  could you please give some

advices on them:

quoted

1. Introduce bootopt of 'poweroff=efi'
     Set the pm_power_off to efi_power_off no matter whether there is
_S5 or not

2. Introduce /sys/power/poweroff
    Allow the user to choose which  pm_power_off, for example:

# cat /sys/power/poweroff
*acpi		acpi_power_off
efi		efi_power_off
gpio		gpio_poweroff_do_poweroff
user can echo string to enable which one.

And two APIs:
register_power_off(char *name, power_off func)
unregister_power_off(char *name)


3. replace all the codes of  pm_power_off() with
reliable_pm_power_off()

void reliable_pm_power_off(void)
{
	if (!pm_power_off) {
		if (acpi_no_s5)
			pm_power_off = efi_power_off;
	/* Other conditions added in the future. */
	}
	pm_power_off();
}

Be wary of adding all these control knobs. People just want their machines to
reboot properly without having to mess with boot parameters.

Let's go back to the start. What prompted this patch? Do Intel have (or are
planning) machines that do not have _S5 and are expected to use EFI to reset
the system? 

Yes, there might be a new platform without _S5, and might need EFI poweroff
for a backup.

Or is this some new configuration discussed in the ACPI spec
that Linux needs to be support?

Can we remove the ambiguity and options to force EFI reset if _S5 is missing?
Afterall, that's why the function is called efi_poweroff_*required*.

OK, the boot option is obsoleted, I'll try another version of default_power_off per
Rafael's suggestion, thanks.

yu