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

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Message-ID: <20160317143926.GL2619@codeblueprint.co.uk>
Date:	Thu, 17 Mar 2016 14:39:26 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	"Chen, Yu C" <yu.c.chen@...el.com>
Cc:	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Mark Salter <msalter@...hat.com>
Subject: 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,
> 
> > -----Original Message-----
> > From: Matt Fleming [mailto:matt@...eblueprint.co.uk]
> > Sent: Tuesday, March 15, 2016 4:01 AM
> > To: Chen, Yu C
> > Cc: linux-acpi@...r.kernel.org; linux-pm@...r.kernel.org; Rafael J. Wysocki;
> > Len Brown; Thomas Gleixner; Ingo Molnar; H. Peter Anvin; Zhang, Rui; linux-
> > efi@...r.kernel.org; x86@...nel.org; linux-kernel@...r.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:
> > >
> > > 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).