linux-kernel - Re: [Resend][PATCH 1/9] ACPI: Implement the set_target() callback from pm

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Date:	Sat, 21 Jul 2007 12:26:30 -0700
From:	David Brownell <david-b@...bell.net>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Len Brown <len.brown@...el.com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>, Shaohua Li <shaohua.li@...el.com>,
	Johannes Berg <johannes@...solutions.net>,
	Paul Mackerras <paulus@...ba.org>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [Resend][PATCH 1/9] ACPI: Implement the set_target() callback from pm_ops

On Tuesday 17 July 2007, Rafael J. Wysocki wrote:
> In the future some drivers may need to use ACPI to determine the low power
> states in which to place their devices, but to provide the drivers with this
> information the ACPI core needs to know what sleep state the system is going to
> enter.  Namely, the device's state should not be too high power for given system
> sleep state and, if the device is supposed to be able to wake up the system, its
> state should not be too low power for the wake up to be possible).  For this
> purpose, the ACPI core needs to implement the set_target() method in 'struct
> pm_ops' and store the target system sleep state passed by the PM core in a
> variable.

Modulo Len's "please remove non-existent S2 state", ACK.

We still have a general issue that most platforms implement
at most one of the sleep states the hardware allows (plus,
sometimes, hibernation).

A key differentiator of those different sleep states is usually
that they have characteristics which allow various devices to
work, or not.  Like, oh, USB controllers which need a 48 MHz
oscillator to process wakeup events ... but the deepest sleep
states must disable that oscillator.

So it's a Good Thing that this patch (and #2) expose that more
complete model of system sleep states to drivers running on x86.

- Dave
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