Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759097Ab1FVWSW (ORCPT ); Wed, 22 Jun 2011 18:18:22 -0400 Received: from na3sys009aog113.obsmtp.com ([74.125.149.209]:47718 "EHLO na3sys009aog113.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759081Ab1FVWSU (ORCPT ); Wed, 22 Jun 2011 18:18:20 -0400 From: Kevin Hilman To: "Rafael J. Wysocki" Cc: Linux PM mailing list , "Greg Kroah-Hartman" , Magnus Damm , Paul Walmsley , Alan Stern , LKML , linux-sh@vger.kernel.org Subject: Re: [Update][PATCH 7/8] PM / Domains: System-wide transitions support for generic domains (v3) Organization: Texas Instruments, Inc. References: <201106112223.04972.rjw@sisk.pl> <201106200006.07642.rjw@sisk.pl> <8739j1lemc.fsf@ti.com> <201106230016.46704.rjw@sisk.pl> Date: Wed, 22 Jun 2011 15:18:17 -0700 In-Reply-To: <201106230016.46704.rjw@sisk.pl> (Rafael J. Wysocki's message of "Thu, 23 Jun 2011 00:16:46 +0200") Message-ID: <871uyljys6.fsf@ti.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2669 Lines: 57 "Rafael J. Wysocki" writes: > On Wednesday, June 22, 2011, Kevin Hilman wrote: >> "Rafael J. Wysocki" writes: >> >> > From: Rafael J. Wysocki >> > >> > Make generic PM domains support system-wide power transitions >> > (system suspend and hibernation). Add suspend, resume, freeze, thaw, >> > poweroff and restore callbacks to be associated with struct >> > generic_pm_domain objects and make pm_genpd_init() use them as >> > appropriate. >> > >> > The new callbacks do nothing for devices belonging to power domains >> > that were powered down at run time (before the transition). >> >> Great, this is the approach I prefer too, but... >> >> Now I'm confused. Leaving runtime suspended devices alone is what I was >> doing in my subsystem but was told not to. According to >> >> http://www.mail-archive.com/linux-omap@vger.kernel.org/msg50690.html >> >> "it's generally agreed that _all_ devices should return to full >> power during system resume -- even if they were runtime suspended >> before the system sleep." > > Well, let's say this part of the documentation is slightly outdated. > > It basically refers to the model in which system suspend is a separate global > hardware or firmware operation, so the state of devices may be changed by the > BIOS or whatever takes over control in the meantime. In that case the kernel > has to ensure that the states of devices are consistent with what it thinks > about them and the simplest way to achieve that is to put the devices to > full power during resume (and back to low power if that's desirable). > > However, in the case of the systems this patchset is intended for system > suspend is achieved by putting various hardware components into low-power > states directly in a coordinated way and the system sleep state effectively > follows from the low-power states the hardware components end up in. The > system is woken up from this state by an interrupt or another mechanism under > the kernel's control. As a result, the kernel never gives control away, so > the state of devices after the resume is precisely known to it. > In consequence, it need not ensure that the state of devices is consistent with > its view, because it knows that this is the case. :-) > > So the documentation should be updated to say what hardware model it is > referring to. Great! Thanks for the clarification. Kevin -- 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/