From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753312AbcKNNsn (ORCPT ); Mon, 14 Nov 2016 08:48:43 -0500 Received: from mx2.suse.de ([195.135.220.15]:52660 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932233AbcKNNsf (ORCPT ); Mon, 14 Nov 2016 08:48:35 -0500 Date: Mon, 14 Nov 2016 14:48:32 +0100 From: "Luis R. Rodriguez" To: Lukas Wunner Cc: "Luis R. Rodriguez" , "Rafael J. Wysocki" , Linux PM list , Greg Kroah-Hartman , Alan Stern , Linux Kernel Mailing List , Tomeu Vizoso , Mark Brown , Marek Szyprowski , Kevin Hilman , Ulf Hansson , Grant Likely , Laurent Pinchart , Lars-Peter Clausen , Andrzej Hajda Subject: Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support Message-ID: <20161114134831.GX13978@wotan.suse.de> References: <27296716.H9VWo8ShOm@vostro.rjw.lan> <13957403.ZrB4mMbICz@vostro.rjw.lan> <2715729.9U1nlcpFb3@vostro.rjw.lan> <20161107213954.GI1764@wotan.suse.de> <20161113173413.GB9598@wunner.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161113173413.GB9598@wunner.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 13, 2016 at 06:34:13PM +0100, Lukas Wunner wrote: > On Mon, Nov 07, 2016 at 10:39:54PM +0100, Luis R. Rodriguez wrote: > > On Mon, Oct 10, 2016 at 02:51:04PM +0200, Rafael J. Wysocki wrote: > > > One of the actions carried out by device_link_add() is to reorder > > > the lists used for device shutdown and system suspend/resume to > > > put the consumer device along with all of its children and all of > > > its consumers (and so on, recursively) to the ends of those lists > > > in order to ensure the right ordering between all of the supplier > > > and consumer devices. > > > > There's no explanation as to why this order is ensured to be > > correct, I think its important to document this. From our discussions > > at Plumbers it seems the order is ensured due to the fact that order > > was already implicitly provided through platform firmware (ACPI > > enumeration is one), adjusting order on the dpm list is just shuffling > > order between consumer / provider, but nothing else. > > ACPI specifies a hierarchy and the order on the dpm_list and > devices_kset is such that children are behind their parent. > > A device link specifies a dependency that exists in addition > to the hierarchy, hence consumers need to be moved behind > their supplier. And not only the consumers themselves but > also recursively their children and consumers. Essentially > the entire subtree is moved to the back. That happens in > device_reorder_to_tail() in patch 2. Ah neat, I failed to notice this full subtree tree move, its rather important. > If another device is enumerated which acts as a supplier to > an existing other supplier, that other supplier and all its > dependents are moved behind the newly enumerated device, > and so on. > > That is probably correct so long as no loops are introduced > in the dependency graph. "Probably" is what concerns me, there is no formality about the correctness of this. > That is checked by device_is_dependent(), > which is called from device_link_add(), and the addition of the > link is aborted if a loop is detected. And that is sufficient ? Luis