Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754616Ab0F1MwC (ORCPT ); Mon, 28 Jun 2010 08:52:02 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:56099 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754423Ab0F1MwA (ORCPT ); Mon, 28 Jun 2010 08:52:00 -0400 From: "Rafael J. Wysocki" To: markgross@thegnar.org Subject: Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost Date: Mon, 28 Jun 2010 14:50:10 +0200 User-Agent: KMail/1.13.3 (Linux/2.6.35-rc3-rjw+; KDE/4.4.3; x86_64; ; ) Cc: linux-pm@lists.linux-foundation.org, Alan Stern , Linux Kernel Mailing List , Neil Brown , Matthew Garrett , mark gross <640e9920@gmail.com>, Arve =?iso-8859-1?q?Hj=F8nnev=E5g?= , Dmitry Torokhov , Florian Mickler , linux-pci@vger.kernel.org, Jesse Barnes References: <201006261514.13491.rjw@sisk.pl> <20100627222804.GA5522@gvim.org> In-Reply-To: <20100627222804.GA5522@gvim.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201006281450.11285.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3264 Lines: 66 On Monday, June 28, 2010, mark gross wrote: > Looks good to me! Great, thanks! May I add your "Acked-by" to the patch, then? Rafael > On Sat, Jun 26, 2010 at 03:14:13PM +0200, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki > > > > One of the arguments during the suspend blockers discussion was that > > the mainline kernel didn't contain any mechanisms making it possible > > to avoid losing wakeup events during system suspend. > > > > Generally, there are two problems in that area. First, if a wakeup > > event occurs exactly when /sys/power/state is being written to, it > > may be delivered to user space right before the freezer kicks in, so > > the user space consumer of the event may not be able to process it > > before the system is suspended. Second, if a wakeup event occurs > > after user space has been frozen, it is not generally guaranteed that > > the ongoing transition of the system into a sleep state will be > > aborted. > > > > To address these issues introduce a new global sysfs attribute, > > /sys/power/wakeup_count, associated with a running counter of wakeup > > events and three helper functions, pm_stay_awake(), pm_relax(), and > > pm_wakeup_event(), that may be used by kernel subsystems to control > > the behavior of this attribute and to request the PM core to abort > > system transitions into a sleep state already in progress. > > > > The /sys/power/wakeup_count file may be read from or written to by > > user space. Reads will always succeed (unless interrupted by a > > signal) and return the current value of the wakeup events counter. > > Writes, however, will only succeed if the written number is equal to > > the current value of the wakeup events counter. If a write is > > successful, it will cause the kernel to save the current value of the > > wakeup events counter and to abort the subsequent system transition > > into a sleep state if any wakeup events are reported after the write > > has returned. > > > > [The assumption is that before writing to /sys/power/state user space > > will first read from /sys/power/wakeup_count. Next, user space > > consumers of wakeup events will have a chance to acknowledge or > > veto the upcoming system transition to a sleep state. Finally, if > > the transition is allowed to proceed, /sys/power/wakeup_count will > > be written to and if that succeeds, /sys/power/state will be written > > to as well. Still, if any wakeup events are reported to the PM core > > by kernel subsystems after that point, the transition will be > > aborted.] > > > > Additionally, put a wakeup events counter into struct dev_pm_info and > > make these per-device wakeup event counters available via sysfs, > > so that it's possible to check the activity of various wakeup event > > sources within the kernel. > > > > To illustrate how subsystems can use pm_wakeup_event(), make the > > low-level PCI runtime PM wakeup-handling code use it. > > > > Signed-off-by: Rafael J. Wysocki > > --- -- 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/