linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902240053.11164.rjw@sisk.pl>
Date:	Tue, 24 Feb 2009 00:53:08 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Tuesday 24 February 2009, Arve Hjønnevåg wrote:
> On Sat, Feb 21, 2009 at 12:20 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Saturday 21 February 2009, Arve Hjønnevåg wrote:
> >> On Sat, Feb 21, 2009 at 1:47 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> > On Saturday 21 February 2009, Arve Hjønnevåg wrote:
> >> >> On Fri, Feb 20, 2009 at 3:57 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> >> > On Saturday 21 February 2009, Arve Hjønnevåg wrote:
> >> >> >> On Fri, Feb 20, 2009 at 7:56 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> >> >> > On Friday 20 February 2009, Arve Hjønnevåg wrote:
> >> >> >> >> On Fri, Feb 20, 2009 at 2:49 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> >> >> >> > On Friday 20 February 2009, Arve Hjønnevåg wrote:
> >> >> >> >> >> On Thu, Feb 19, 2009 at 2:08 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> > [--snip--]
> >> >> > The idea is to have both /sys/power/state and /sys/power/sleep at the same
> >> >> > time, where /sys/power/state will work just like it does right now.  Sure,
> >> >> > there must be mutual exclusion between the two, but that's a matter of
> >> >> > implementation IMO.
> >> >>
> >> >> If you want to only prevent suspend though one interface, you have to
> >> >> also pass information to the driver about its suspend hook is being
> >> >> called so it can conditionally return -EBUSY. The wakelock interface
> >> >> requires less code in each driver.
> >> >
> >> > Well, I don't think so.  Moreover, it requires you to spread wakelocks all
> >> > over the place if you don't use the timeouted ones which, let's face it, is
> >> > hardly acceptable.
> >>
> >> Your method does not reduce the number of places that has to be
> >> modified. Any component where we add a wakelock, you have to add a
> >> suspend handler to abort suspend when we would have held a wakelock.
> >
> > Well, maybe not, but it doesn't introduce entirely new API for device drivers.
> > Instead, it extends the existing interfaces which I think is more appropriate.
> 
> The existing interfaces require polling. I don't think extending these
> interfaces to make the polling faster is a better solution than adding
> an interface to avoid polling.
> 
> Also, with your solution, how would you modify evdev.c to prevent
> suspend while the event queue is not empty. This code does not have
> any suspend hooks and the queue is not tied to any thread.

Well, why do you need to modify evdev.c in the first place?

Rafael
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