linux-kernel - Re: [PATCH 0/8] Suspend block api (version 6)

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Message-ID: <20100504004338.GA22678@srcf.ucam.org>
Date:	Tue, 4 May 2010 01:43:38 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	Kevin Hilman <khilman@...prootsystems.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Paul Walmsley <paul@...an.com>, magnus.damm@...il.com,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 6)

On Mon, May 03, 2010 at 04:37:22PM -0700, Kevin Hilman wrote:

> Please forgive the ignorance of ACPI (in embedded, we thankfully live
> in magical world without ACPI) but doesn't that already happen with
> CPUidle and C-states?  I think of CPUidle as basically runtime PM for
> the CPU.  IOW, runtime PM manages the devices, CPUidle manages the CPU
> (via C-states), resulting in dynaimc PM for the entire system.  What
> am I missing?

ACPI doesn't provide any functionality for cutting power to most devices 
other than shifting into full system suspend. The number of wakeup 
events available to us on a given machine is usually small and the 
wakeup latency large, so it's not terribly practical to do this 
transparently on most hardware.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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