linux-kernel - Re: [PATCH v2] Add suspend/resume for HPET

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Date:	Sat, 31 Mar 2007 09:53:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Maxim Levitsky <maximlevitsky@...il.com>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ingo Molnar <mingo@...e.hu>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, pavel@...e.cz,
	linux-pm@...ts.osdl.org, gregkh@...e.de,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Jens Axboe <jens.axboe@...cle.com>,
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	jgarzik@...ox.com, linux-ide@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...lanox.co.il>
Subject: Re: [PATCH v2] Add suspend/resume for HPET

On Sat, 31 Mar 2007, Thomas Gleixner wrote:
> 
> Right, but clock - sources/events need to be extremly late suspended and
> early resumed. How can we ensure this ?

Make them be at the top of the device tree by adding them early. That's 
the whole point of the device tree after all - we have an ordering that is 
enforced by its topology, and that we sort by when things were added.

Right now the way things work is (iirc - somebody like Greg should 
double-check me) is that we add all devices to the power list at 
device_add() time by traversing the devices fromt he root all the way out, 
and doing a device_add() which does a device_pm_add(), which in turn adds 
it to the power-management list - so that the list is always topologically 
sorted.

So the only thing that needs to be done is to make sure that we add the 
timer devices early during bootup - something we have to do *anyway*. If a 
device is added early in bootup, that automatically means that it will be 
suspended late, and resumed early - because we maintain that order all the 
way through..

		Linus
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