From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754888AbbGCOQ1 (ORCPT ); Fri, 3 Jul 2015 10:16:27 -0400 Received: from netrider.rowland.org ([192.131.102.5]:40556 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754984AbbGCOQU (ORCPT ); Fri, 3 Jul 2015 10:16:20 -0400 Date: Fri, 3 Jul 2015 10:16:19 -0400 (EDT) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: Tomeu Vizoso cc: "linux-pm@vger.kernel.org" , Laurent Pinchart , Dmitry Torokhov , "Rafael J. Wysocki" , 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: 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 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. > >> > 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. > 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. Alan Stern