From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kevin Hilman <khilman@deeprootsystems.com>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)
Date: Fri, 14 May 2010 09:18:15 -0700
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In-Reply-To: <AANLkTilL2mvqpwirTfJRWZFdrFJvSihnaY8-xao4pLpH@mail.gmail.com> (Magnus Damm's message of "Fri\, 14 May 2010 12\:25\:26 +0900")
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To: Magnus Damm <magnus.damm@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>, Alan Stern <stern@rowland.harvard.edu>, Paul Walmsley <paul@pwsan.com>, Arve =?iso-8859-1?Q?Hj=F8nnev=E5g?= <arve@android.com>, Linux-pm mailing list <linux-pm@lists.linux-foundation.org>, Kernel development list <linux-kernel@vger.kernel.org>, Tejun Heo <tj@kernel.org>, Oleg Nesterov <oleg@redhat.com>, Theodore Ts'o <tytso@mit.edu>, mark gross <mgross@linux.intel.com>, Arjan van de Ven <arjan@infradead.org>, Geoff Smith <geoffx.smith@intel.com>, Brian Swetland <swetland@google.com>, "Rafael J. Wysocki" <rjw@sisk.pl>, Matthew Garrett <mjg@redhat.com>, =?iso-8859-1?Q?Beno=EEt?= Cousson <b-cousson@ti.com>, linux-omap@vger.kernel.org, Vitaly Wool <vitalywool@gmail.com>, Linus Walleij <linus.walleij@ericsson.com>, Mark Brown <broonie@opensource.wolfsonmicro.com>, Liam Girdwood <lrg@slimlogic.co.uk>
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Magnus Damm <magnus.damm@gmail.com> writes:

> Still not sure how the system wide suspend is different from Runtime
> PM and CPUidle from the hardware perspective...

At least on OMAP and other embedded SoCs I'm familiar with, there is
no difference from the hardware perspecitve.

However, I understand that on ACPI-based systems, there are low-power
that are only reachable via system-wide suspsend since ACPI does not
provide the kernel with fine-grained control to hit those states
during idle.

That being said, I don't think this should be an issue since
opportunistic suspend is currently targetted primarily at embedded HW
which has much more fine-grained power control than traditional
ACPI-based systems.

To me the only real difference between system-wide suspend and runtime
PM + CPUidle is the freezing of userspace.

As has been discussed elsewhere in this discussion, any alternative
solution must address the freezing/idling of userspace.  

Kevin