Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933063Ab1DMQPl (ORCPT ); Wed, 13 Apr 2011 12:15:41 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:34135 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932360Ab1DMQPh convert rfc822-to-8bit (ORCPT ); Wed, 13 Apr 2011 12:15:37 -0400 MIME-Version: 1.0 In-Reply-To: References: <201104130205.26988.rjw@sisk.pl> From: Grant Likely Date: Wed, 13 Apr 2011 10:15:16 -0600 X-Google-Sender-Auth: sGLFEtOrN8x9AYm0WctvUdB3hUM Message-ID: Subject: Re: [RFC][PATCH] PM: Make power domain callbacks take precedence over subsystem ones To: Alan Stern Cc: "Rafael J. Wysocki" , Linux PM mailing list , Kevin Hilman , LKML , Len Brown , linux-sh@vger.kernel.org, lethal@linux-sh.org, Magnus Damm Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2988 Lines: 60 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. g. -- 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/