Subject: Re: [PATCH 3/3 -mm] kexec based hibernation -v6: kexec
	hibernate/resume
From: "Huang, Ying" <ying.huang@intel.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Pavel Machek <pavel@ucw.cz>,
       nigel@nigel.suspend2.net, Andrew Morton <akpm@linux-foundation.org>,
       Jeremy Maitin-Shepard <jbms@cmu.edu>, linux-kernel@vger.kernel.org,
       linux-pm@lists.linux-foundation.org,
       Kexec Mailing List <kexec@lists.infradead.org>
In-Reply-To: <200711210100.32631.rjw@sisk.pl>
References: <1195455769.10291.26.camel@caritas-dev.intel.com>
	 <200711200324.31180.rjw@sisk.pl>
	 <1195527033.11955.50.camel@caritas-dev.intel.com>
	 <200711210100.32631.rjw@sisk.pl>
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Date: Wed, 21 Nov 2007 16:05:06 +0800
Message-Id: <1195632306.29280.7.camel@caritas-dev.intel.com>
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On Wed, 2007-11-21 at 01:00 +0100, Rafael J. Wysocki wrote:
> On Tuesday, 20 of November 2007, Huang, Ying wrote:
> > On Tue, 2007-11-20 at 03:24 +0100, Rafael J. Wysocki wrote:
> > > On Tuesday, 20 of November 2007, Huang, Ying wrote:
> > > > On Mon, 2007-11-19 at 19:22 +0100, Rafael J. Wysocki wrote:
> > > > > > +#ifdef CONFIG_KEXEC
> > > > > > +static void kexec_hibernate_power_down(void)
> > > > > > +{
> > > > > > +	switch (hibernation_mode) {
> > > > > > +	case HIBERNATION_TEST:
> > > > > > +	case HIBERNATION_TESTPROC:
> > > > > > +		break;
> > > > > > +	case HIBERNATION_REBOOT:
> > > > > > +		machine_restart(NULL);
> > > > > > +		break;
> > > > > > +	case HIBERNATION_PLATFORM:
> > > > > > +		if (!hibernation_ops)
> > > > > > +			break;
> > > > > > +		hibernation_ops->enter();
> > > > > 
> > > > > hibernation_platform_enter() should be used here (as of the current mainline).
> > > > 
> > > > The power_down will be called with interrupt disabled, device suspended,
> > > > non-boot CPU disabled. But the latest hibernate_platform_enter calls the
> > > > device_suspend, disable_nonboot_cpus etc function. So, I use
> > > > hibernation_ops->enter() directly instead of
> > > > hibernation_platform_enter().
> > > 
> > > Hm, you need to call device_power_down(PMSG_SUSPEND) before
> > > hibernation_ops->enter().
> > > 
> > > Also, all of the ACPI global calls need to be carried out before that and the
> > > devices should be suspended rather than shut down in that case.
> > > 
> > > That's why hibernation_platform_enter() has been introduced, BTW.
> > 
> > Situation is a little different between u/swsusp and khiberantion.
> > 
> > u/swsusp:
> > 
> > platform_start();
> > suspend console();
> > device_suspend(PMSG_FREEZE);
> > platform_pre_snapshot();
> > disable_nonboot_cpus();
> > local_irq_disable();
> > device_power_down(PMSG_FREEZE);
> > /* create snapshot */
> > device_power_up();
> > local_irq_enable();
> > enable_nonboot_cpus();
> > platform_finish();
> > device_resume();
> > resume_console();
> > /* write the image out */
> > hibernation_ops->start();
> > suspend_console();
> > device_suspend(PMSG_SUSPEND);
> > hibernation_ops->prepare();
> > disable_nonboot_cpus();
> > local_irq_disable();
> > device_power_down(PMSG_SUSPEND);
> > hibernation_ops->enter();
> > 
> > khibernation:
> > 
> > suspend_console();
> > platform_start();
> > device_suspend(PMSG_FREEZE);
> > platform_pre_snapshot();
> > disable_nonboot_cpus();
> > local_irq_disable();
> > device_power_down(PMSG_FREEZE);
> > /* jump to kexeced (hibernating) kernel */
> > /* in kexeced kernel */
> > device_power_up();
> > local_irq_eanble();
> > enable_nonboot_cpus();
> 
> You should call platform_finish() here, or device_resume() will not work
> appropriately on some systems.
> 
> However, after platform_finish() has been executed, the ACPI firmware will
> assume that the hibernation has been canceled, so you need to tell it that
> you'd like to go into the low power state after all.
> 
> > device_resume();
> > resume_console();
> > /* write the image */
> 
> For this reason, you have to call hibernation_ops->start() once again
> and the other functions like in the swsusp case, in that order.
> 
> > suspend_console();
> > device_suspend(PMSG_FREEZE);
> > disable_nonboot_cpus();
> > local_irq_disable();
> > device_power_down(PMSG_FREEZE);
> > /* jump to original (hibernated) kernel */
> 
> This looks too fragile to my eyes.
> 
> Why don't you call hibernation_ops->enter() directly from the "kexeced" kernel?

I don't know whether there are ACPI global state inside Linux kernel. So
I restrict all ACPI method calling in original kernel. If the ACPI
global state in Linux kernel is not a issue, I can call
hibernation_ops->enter() directly in the "kexeced" kernel.

Best Regards,
Huang Ying
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