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

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Message-ID: <Pine.LNX.4.44L0.1110141156040.2036-100000@iolanthe.rowland.org>
Date:	Fri, 14 Oct 2011 12:00:59 -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 Fri, 14 Oct 2011, NeilBrown wrote:

> Hi Rafael,
> 
>  What do you mean by "too complicated to use in practice"?  What is you
>  measure for complexity?
>  Using suspend in a race-free way is certainly less complex than - for
>  example - configuring bluetooth.
>  And in what way is it "inadequate for other reasons"? What reasons?
> 
> 
>  The only sane way to handle suspend is for any (suitably privileged) process
>  to be able to request that suspend doesn't happen, and then for one process
>  to initiate suspend when no-one is blocking it.

One of the things Rafael didn't mention is that sometimes a kernel 
driver needs to prevent the system from suspending.  This happens when 
recharging over a USB connection.

There's no simple way for such a driver to communicate with a power
daemon.  The driver has to use something like the wakeup mechanism -- 
but currently that mechanism is optional.

Alan Stern

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