Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754658Ab1DNXME (ORCPT ); Thu, 14 Apr 2011 19:12:04 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:52164 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754472Ab1DNXMB (ORCPT ); Thu, 14 Apr 2011 19:12:01 -0400 From: "Rafael J. Wysocki" To: Grant Likely Subject: Re: [RFC][PATCH] PM: Make power domain callbacks take precedence over subsystem ones Date: Fri, 15 Apr 2011 01:12:24 +0200 User-Agent: KMail/1.13.6 (Linux/2.6.39-rc3+; KDE/4.6.0; x86_64; ; ) Cc: Alan Stern , Linux PM mailing list , Kevin Hilman , LKML , Len Brown , linux-sh@vger.kernel.org, lethal@linux-sh.org, Magnus Damm References: <201104130205.26988.rjw@sisk.pl> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201104150112.24722.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3231 Lines: 66 On Wednesday, April 13, 2011, Grant Likely wrote: > On Wed, Apr 13, 2011 at 8:17 AM, Alan Stern wrote: > > On Wed, 13 Apr 2011, Rafael J. Wysocki wrote: > > > >> From: Rafael J. Wysocki > >> > >> Change the PM core's behavior related to power domains in such a way > >> that, if a power domain is defined for a given device, its callbacks > >> will be executed instead of and not in addition to the device > >> subsystem's PM callbacks. > >> > >> The idea behind the initial implementation of power domains handling > >> by the PM core was that power domain callbacks would be executed in > >> addition to subsystem callbacks, so that it would be possible to > >> extend the subsystem callbacks by using power domains. It turns out, > >> however, that this wouldn't be really convenient in some important > >> situations. > >> > >> For example, there are systems in which power can only be removed > >> from entire power domains. On those systems it is not desirable to > >> execute device drivers' PM callbacks until it is known that power is > >> going to be removed from the devices in question, which means that > >> they should be executed by power domain callbacks rather then by > >> subsystem (e.g. bus type) PM callbacks, because subsystems generally > >> have no information about what devices belong to which power domain. > >> Thus, for instance, if the bus type in question is the platform bus > >> type, its PM callbacks generally should not be called in addition to > >> power domain callbacks, because they run device drivers' callbacks > >> unconditionally if defined. > > > > What about systems where it makes sense to execute the subsystem > > callbacks even if power isn't going to be removed from the device? > > It's quite possible that the subsystem could reduce the device's power > > consumption even when the device isn't powered down completely. > > The understanding Rafael and I came to was that if a power domain is > attached to a device, then the power domain becomes the responsible > party. Normally this means it will turn around and immediately call > the bus_type pm ops, but it has the option to not call them if for a > particular system it knows better, or to defer calling them. > > Basically, if you're using a power domain, it is assumed that the > power domain has particular knowledge about the system, and it should > have the option to override the default behaviour. > > > > > Is the extra overhead of invoking the subsystem callback really all > > that troublesome? > > It isn't an overhead problem. It's a control & complexity problem. > We could try to implement a heuristic or api to control when the bus > type PM ops should be overridden, but I think it is cleaner to make it > a rule that if you implement a power domain, then that power domain > becomes responsible for all PM operations. Well said. :-) I'm taking that as an ACK for my patch if you don't mind. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/