Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966001AbbD1O1F (ORCPT ); Tue, 28 Apr 2015 10:27:05 -0400 Received: from mail-qk0-f178.google.com ([209.85.220.178]:34167 "EHLO mail-qk0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965693AbbD1O1A (ORCPT ); Tue, 28 Apr 2015 10:27:00 -0400 MIME-Version: 1.0 In-Reply-To: References: From: Tomeu Vizoso Date: Tue, 28 Apr 2015 16:26:39 +0200 X-Google-Sender-Auth: bX8PSIeA0B4KnZbFVIbzZKWlAQI Message-ID: Subject: Re: [PATCH v3 1/2] PM / sleep: Let devices force direct_complete To: Alan Stern Cc: Laurent Pinchart , "linux-pm@vger.kernel.org" , Dmitry Torokhov , "Rafael J. Wysocki" , Pavel Machek , Len Brown , Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" 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: 3319 Lines: 73 On 20 April 2015 at 16:12, Alan Stern wrote: > On Mon, 20 Apr 2015, Tomeu Vizoso wrote: > >> On 17 April 2015 at 19:30, Alan Stern wrote: >> > On Fri, 17 Apr 2015, Laurent Pinchart wrote: >> > >> >> Hi Tomeu, >> >> >> >> Thank you for the patch. >> >> >> >> On Friday 17 April 2015 17:24:49 Tomeu Vizoso wrote: >> >> > Introduce a new per-device flag power.force_direct_complete that will >> >> > instruct the PM core to ignore the runtime PM status of its descendants >> >> > when deciding whether to let this device remain in runtime suspend when >> >> > the system goes into a sleep power state. >> >> > >> >> > This is needed because otherwise it would be needed to get dozens of >> >> > drivers to implement the prepare() callback and be runtime PM active >> >> > even if they don't have a 1-to-1 relationship with a piece of HW. >> >> >> >> I'll let PM experts comment on the approach, but I believe the new flag would >> >> benefit from being documented (likely in Documentation/power/devices.txt) :-) >> > >> > Documentation/power/runtime_pm.txt is the right place. >> > >> > However, I'm not sure that this is the sort of thing Rafael meant when >> > he suggested adding a new flag. I thought he meant the PM core would >> > look at the new flag only if there was no ->prepare method at all. >> > Then if the new flag was set, the PM core would act as though ->prepare >> > had returned 1. That way there would be no need to add silly little >> > one-line *_prepare() routines all over the place. >> > >> > Maybe he had something else in mind, though... >> >> Yeah, I also interpreted it like that, but when I started looking at >> how it would work, I found that it would be awkward if the uvcvideo >> driver had to track all the devices that get attached below its >> devices in order to set that flag to them. >> >> When thinking about it, it occurred to me that it may make more sense >> if we model this as a property of the device bound to the uvcvideo >> driver, as what's happening here is that the uvcvideo driver knows >> that it's safe to remain in runtime suspend when the system goes to >> sleep, and that all its descendant devices can be ignored in that >> regard. > > What you're proposing makes sense, but it is a significant change to > the runtime PM core. It should be submitted separately, not as part of > an update to the UVC driver, and it should be discussed at length. > > Basically, you want to mark certain devices to say that they will > _always_ use direct-suspend. This means that all descendant devices > will be forced to use direct-suspend also, and therefore any driver > bound to one of these descendant devices will be unable to communicate > with it during a system sleep transition. This is a non-trivial > restriction. > > Among other things, it means that wakeup settings can't be altered > during a sleep transition. Therefore this should be allowed only for > devices that are not wakeup-capable. Hi Rafael, do you have any comments on this? Thanks, Tomeu -- 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/