Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755911AbbGDAFP (ORCPT ); Fri, 3 Jul 2015 20:05:15 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:56868 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755576AbbGDAFG (ORCPT ); Fri, 3 Jul 2015 20:05:06 -0400 From: "Rafael J. Wysocki" To: Tomeu Vizoso Cc: Alan Stern , "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 Date: Sat, 04 Jul 2015 02:31:27 +0200 Message-ID: <1564143.gqjAhPtVFo@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4395 Lines: 100 On Friday, July 03, 2015 04:22:02 PM Tomeu Vizoso wrote: > On 3 July 2015 at 16:16, Alan Stern wrote: > > On Fri, 3 Jul 2015, Tomeu Vizoso wrote: > > > >> On 2 July 2015 at 17:21, Alan Stern wrote: > >> > On Thu, 2 Jul 2015, Tomeu Vizoso wrote: > >> > > >> >> > Just because these sub-devices are virtual, it doesn't mean you can > >> >> > ignore the way they interact with runtime PM. > >> >> > >> >> Fair enough, but then, how are we expected to be able to use the > >> >> direct_complete facility if the core bails out if a descendant doesn't > >> >> have runtime PM enabled? > >> >> > >> >> > In the case of ep_87 this doesn't matter. Endpoint devices (like all > >> >> > devices) are in the SUSPENDED state by default when they are created, > >> >> > and they never leave that state. > >> >> > >> >> I don't see why it doesn't matter for endpoints or the others. They > >> >> don't have runtime PM enabled, so no ancestor will be able to do > >> >> direct_complete. > >> > > >> > Ah, you're concerned about these lines near the start of > >> > __device_suspend(): > >> > > >> > if (dev->power.direct_complete) { > >> > if (pm_runtime_status_suspended(dev)) { > >> > pm_runtime_disable(dev); > >> > if (pm_runtime_suspended_if_enabled(dev)) > >> > goto Complete; > >> > > >> > pm_runtime_enable(dev); > >> > } > >> > dev->power.direct_complete = false; > >> > } > >> > > >> > 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? > >> >> > A possible way around the problem is to use pm_suspend_ignore_children > >> >> > on the uvcvideo interface. But I'm not sure that would be the right > >> >> > thing to do. > >> >> > >> >> Would that mean that if a device has ignore_children then it could > >> >> still do direct_complete even if its descendants weren't able to? > >> > > >> > I think we could justify that. The ignore_children flag means we can > >> > communicate with the children even when the device is in runtime > >> > suspend, so there's no reason to force the device to leave runtime > >> > suspend during a system sleep. > >> > >> IIUIC, what you are proposing is to use ignore_children in a way > >> similar to how force_direct_complete was used in this patch? > >> > >> http://thread.gmane.org/gmane.linux.power-management.general/60198/focus=60292 > > > > That message doesn't contain a patch. > > The patch is at the top of the thread: > > http://thread.gmane.org/gmane.linux.power-management.general/60198/focus=60292 > > >> That should work as well, but Rafael raised some objections and thus I > >> went with the present direct_complete_default, which should work if we > >> can relax the check as discussed above. > > > > Rafael and I briefly discussed ignore_children while the original > > direct_complete patch was being designed. We didn't come to any > > definite conclusion and decided to forget about it for the time being. > > Maybe now would be a good time to reconsider it. > > I would prefer to have ignore_children ignore whether the children of > a device were able to do direct_complete, rather than having a > direct_complete_default flag (plus not requiring that all its > descendants have runtime PM enabled). Why? 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/