linux-kernel - Re: Hibernation considerations

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Message-ID: <Pine.LNX.4.64.0707170959160.2467@asgard.lang.hm>
Date:	Tue, 17 Jul 2007 10:06:12 -0700 (PDT)
From:	david@...g.hm
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Alan Stern <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Al Boldi <a1426z@...ab.com>
Subject: Re: Hibernation considerations

On Tue, 17 Jul 2007, Rafael J. Wysocki wrote:

> On Tuesday, 17 July 2007 17:29, david@...g.hm wrote:
>> On Tue, 17 Jul 2007, Rafael J. Wysocki wrote:
>>
>>> On Tuesday, 17 July 2007 16:15, Alan Stern wrote:
>>>> On Mon, 16 Jul 2007 david@...g.hm wrote:
>>>>
>>>>>> I agree, it would be good to have a non-ACPI-specific hibernation mode,
>>>>>> something which would look to ACPI like a normal shutdown.  But I'm not
>>>>>> so sure this is possible.
>>>>>
>>>>> why would it not be possible?
>>>>
>>>>> I can't think of anything much more frustrating then thinking that I
>>>>> suspended a system and then discovering that becouse the battery went dead
>>>>> (a complete power loss) that the system wouldn't boot up properly. to me
>>>>> this would be a fairly common condition (when I'm mobile I use the machine
>>>>> until I am out of battery, then stop and it may be a long time (days)
>>>>> before I can charge the thing up again) this would not be a reliable
>>>>> suspend as far as I'm concerned.
>>>>>
>>>>> for suspend-to-ram you have to worry about ACPI states and what you are
>>>>> doing with them, for suspend-to-disk you can ignore them and completely
>>>>> power the system off instead.
>>>>
>>>> If the only problem with doing this would be lack of wakeup support
>>>> then I'm all for it.  There must be a lot of people who would like
>>>> their computers to hibernate with power drain as close to 0 as possible
>>>> and who don't care about remote wakeup.  In fact they might even prefer
>>>> not to have wakeup support, so the computer doesn't resume at
>>>> unexpected times.
>>>
>>> I'm afraid of one thing, though.
>>>
>>> If we create a framework without ACPI (well, ACPI needs to be enabled in the
>>> kernel anyway for other reasons, like the ability to suspend to RAM) and then
>>> it turns out that we have to add some ACPI hooks to it, that might be difficult
>>> to do cleanly.
>>
>> doing suspend-to-ram should be orthoginal to doing hibernate-to-disk. some
>> people will want both, some won't.
>>
>> at the moment kexec doesn't work with ACPI, that is a limitation that
>> should be fixed, but makeing it able to work with ACPI enabled doesn't
>> mean that it needs to be changed to depend on ACPI and it especially
>> doesn't mean that it should pick up the limitations of the existing ACPI
>> based hibernation approaches.
>>
>> if there is no ACPI on the system it should work, if ther is ACPI on the
>> system it should still work.
>>
>>> Thus, it seems reasonable to think of the ACPI handling in advance.
>>
>> but don't become dependant on ACPI.
>
> Not dependent, but with the possibility of ACPI support taken into account.
>
> Arguably you can create a framework that, for example, will not allow the user
> to adjust the size of the image, but then adding such a functionality may
> require you to change the entire design.  Same thing with ACPI.
>
> I would rather avoid such pitfalls, if I could.

Ok, what is it that you think ACPI fundamentally changes in this process?

keep in mind that we are not makeing the assumption that the hardware 
will remain powered (even a little bit), or the assumption that nothing 
else will run on the hardware (eliminating any possibility that the 
hardware is in a known ACPI state)

David Lang
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