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Date: Tue, 4 May 2010 01:43:38 +0100
From: Matthew Garrett <mjg@redhat.com>
To: Kevin Hilman <khilman@deeprootsystems.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
       Mark Brown <broonie@opensource.wolfsonmicro.com>,
       Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>,
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       magnus.damm@gmail.com, mark gross <mgross@linux.intel.com>,
       Arjan van de Ven <arjan@infradead.org>,
       Geoff Smith <geoffx.smith@intel.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 6)
Message-ID: <20100504004338.GA22678@srcf.ucam.org>
References: <1272667021-21312-1-git-send-email-arve@android.com> <87wrvl5479.fsf@deeprootsystems.com> <20100503180741.GB2098@rakim.wolfsonmicro.main> <201005032318.35383.rjw@sisk.pl> <87sk68r1zh.fsf@deeprootsystems.com>
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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@srcf.ucam.org