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

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Message-ID: <87fx1uo3so.fsf@deeprootsystems.com>
Date:	Fri, 14 May 2010 09:18:15 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	Tony Lindgren <tony@...mide.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Paul Walmsley <paul@...an.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	"Theodore Ts'o" <tytso@....edu>,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>,
	Brian Swetland <swetland@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg@...hat.com>,
	Benoît Cousson <b-cousson@...com>,
	linux-omap@...r.kernel.org, Vitaly Wool <vitalywool@...il.com>,
	Linus Walleij <linus.walleij@...csson.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

Magnus Damm <magnus.damm@...il.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
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