linux-kernel - Re: [RFC][PATCH 0/2] PM / Sleep: Extended control of suspend/hibernate interfaces

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Date:	Mon, 17 Oct 2011 11:43:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	NeilBrown <neilb@...e.de>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux PM list <linux-pm@...r.kernel.org>,
	mark gross <markgross@...gnar.org>,
	LKML <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [RFC][PATCH 0/2] PM / Sleep: Extended control of suspend/hibernate
 interfaces

On Mon, 17 Oct 2011, NeilBrown wrote:

> .... Actually, the more I think about it, the more sense it makes to include
> the wake-up-at-time service with the suspend-daemon.  Then the RTC alarm
> doesn't need a wakeup_source.
> So my hypothetical suspend-daemon provides 2 services:
>  1/ Client can say "Don't suspend after X".  If X is in the past it means
>     don't suspend at all. In the future it means "If you suspend before
>     this, be sure to wake up by X".  This request must be explicitly
>     cancelled (though some mechanism is needed so that if the process dies
>     it is automatically cancelled).
>  2/ Client can say "check with me before entering suspend".  Client needs to
>     respond to any callback promptly, but can register a "don't suspend after
>     now" request first.
>     (Client probably gets a callback both on suspend and resume)

1/ can be a separate type of communication channel to the daemon.  The
client opens a connection and sends the time X.  It then blocks waiting
for a response.  The daemon waits until X (using RTC wakeup alarms as
necessary), then acknowledges the request and prevents further suspends
until the connection is closed.

2/ is the normal client communication mechanism that I described 
earlier.  I don't see why a callback would be needed during resume in 
general, although some clients might want to be informed.

Alan Stern

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