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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>,
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Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)
References: <20100513191717.GA3428@atomide.com>
	<Pine.LNX.4.44L0.1005131729510.1731-100000@iolanthe.rowland.org>
	<20100513214739.GM3428@atomide.com>
	<AANLkTilL2mvqpwirTfJRWZFdrFJvSihnaY8-xao4pLpH@mail.gmail.com>
From: Kevin Hilman <khilman@deeprootsystems.com>
Organization: Deep Root Systems, LLC
Date: Fri, 14 May 2010 09:18:15 -0700
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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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