From: "Chen, Yu C" <yu.c.chen@intel.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
CC: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        Len Brown <lenb@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        "Zhang, Rui" <rui.zhang@intel.com>
Subject: RE: [PATCH][RFC v3] ACPI / PM: Fix poweroff issue on HW-full
 platforms without _S5
Thread-Topic: [PATCH][RFC v3] ACPI / PM: Fix poweroff issue on HW-full
 platforms without _S5
Thread-Index: AQHReBtTuYTrZFDLZkGy2iiQCJLNIJ9NcY+AgACwtaCAACIcAIABZrTQgAEQ+ACAATnd4A==
Date: Thu, 10 Mar 2016 02:25:36 +0000
Message-ID: <36DF59CE26D8EE47B0655C516E9CE640286D3EA6@shsmsx102.ccr.corp.intel.com>
References: <1457319045-25434-1-git-send-email-yu.c.chen@intel.com>
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 <20160309153436.GB15775@codeblueprint.co.uk>
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Hi Matt,

> -----Original Message-----
> From: Matt Fleming [mailto:matt@codeblueprint.co.uk]
> Sent: Wednesday, March 09, 2016 11:35 PM
> To: Chen, Yu C
> Cc: Rafael J. Wysocki; Rafael J. Wysocki; ACPI Devel Maling List;
> x86@kernel.org; linux-efi@vger.kernel.org; Linux Kernel Mailing List; linux-
> pm@vger.kernel.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:
> > 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
> > 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.
> 
> > Currently I'm thinking of 3 possible solutions,  could you please give some
> advices on them:
> >
> > 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