Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752904AbbGEJYy (ORCPT ); Sun, 5 Jul 2015 05:24:54 -0400 Received: from netrider.rowland.org ([192.131.102.5]:42051 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751754AbbGEJYh (ORCPT ); Sun, 5 Jul 2015 05:24:37 -0400 Date: Sat, 4 Jul 2015 10:37:55 -0400 (EDT) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: "Rafael J. Wysocki" cc: Tomeu Vizoso , "linux-pm@vger.kernel.org" , Laurent Pinchart , Dmitry Torokhov , Len Brown , Pavel Machek , Greg Kroah-Hartman , Ulf Hansson , Kevin Hilman , Russell King , Krzysztof Kozlowski , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive In-Reply-To: <1564143.gqjAhPtVFo@vostro.rjw.lan> Message-ID: 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: 2198 Lines: 54 On Sat, 4 Jul 2015, Rafael J. Wysocki wrote: > > >> > Perhaps the pm_runtime_suspended_if_enabled() test should be changed to > > >> > pm_runtime_status_suspended(). Then it won't matter whether the > > >> > descendant devices are enabled for runtime PM. > > >> > > >> Yeah, that would remove the need for messing with the runtime PM > > >> enable status of descendant devices, but I wonder why Rafael went that > > >> way initially. > > > > > > I forget the details. Probably it was just to be safe. We probably > > > thought that if a device was disabled for runtime PM then its runtime > > > PM status might not be accurate. But if direct_complete is set then it > > > may be reasonable to assume that the runtime PM status _is_ accurate. > > > > Cool. > > We're walking a grey area here. What exactly does power.direct_complete mean > for devices whose runtime PM is disabled? > > Let's see what Rafael thinks about these two issues. It seems to me > > that the hardest part is dealing with drivers/subsystems that have no > > runtime PM support. In such cases, we have to be very careful not to > > use direct_complete unless we know that the device does no power > > management at all. > > Precisely. All right, we can make a decision and document it. The following seems reasonable to me: If dev->power.direct_complete is set then the PM core will assume that dev->power.rpm_status is accurate even when dev->power.disable_depth > 0. The core will obey the .direct_complete setting regardless of .disable_depth. As a consequence, devices that support system sleep but don't support runtime PM must _never_ have .direct_complete set. On the other hand, if a device (such as a "virtual" device) requires no callbacks for either system sleep or runtime PM, then there is no harm in setting .direct_complete. Indeed, doing so may help speed up an ancestor device's sleep transition. How does that sound? Alan Stern -- 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/