Re: [PATCH][RFC,v4] ACPI / PM: Introduce efi poweroff for HW-full platforms without _S5

On Wed, 16 Mar, at 05:59:29AM, Chen, Yu C wrote:

Hi Matt,

quoted

-----Original Message-----
From: Matt Fleming [mailto:matt@codeblueprint.co.uk]
Sent: Tuesday, March 15, 2016 4:01 AM
To: Chen, Yu C
Cc: linux-acpi@vger.kernel.org; linux-pm@vger.kernel.org; Rafael J. Wysocki;
Len Brown; Thomas Gleixner; Ingo Molnar; H. Peter Anvin; Zhang, Rui; linux-
efi@vger.kernel.org; x86@kernel.org; linux-kernel@vger.kernel.org; Ard
Biesheuvel; Mark Salter
Subject: Re: [PATCH][RFC,v4] ACPI / PM: Introduce efi poweroff for HW-full
platforms without _S5

On Fri, 11 Mar, at 04:33:46PM, Chen, Yu C wrote:

quoted

There is  a future Base-IA platform, we are planning to skip
implementing the SLP_TYP register and the S5 object.  (already there
will be no S3 and no S4)

Cool. This is really valuable information that should go into the commit
message.

Because if this is the rationale for the change, I don't see why we'd need to
provide the default stuff. Instead we should just enforce EFI reboot, and
only add the pm_poweroff_default hook if there is an explicit user in the
future, IMO.

Do you mean the patch v3 make sense
https://patchwork.kernel.org/patch/8514751/
and we should use efi power off as our first choice, if there is no _S5  available(no acpi_power_off),
even there is a customized  poweroff(driver provided, eg)? 

Unless someone can point to a platform driver that is in the upstream
kernel where this is actually a problem, the answer is: yes.
 
For that matter, unless someone can do the same for pm_power_off
overriding efi_reboot() (which on x86 would only happen for ACPI
HW-reduced platforms), I would be much prefer the original patch,
where you had,

bool efi_poweroff_reqired(voi)
{
	return acpi_gbl_reduced_hardware || acpi_no_s5;
}

since you've already explained that this change won't break legacy
platforms that are missing _S5 (if any even exist in the wild).