From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DDE97C3279B for ; Sun, 8 Jul 2018 13:22:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 995A320881 for ; Sun, 8 Jul 2018 13:22:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 995A320881 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933073AbeGHNWQ (ORCPT ); Sun, 8 Jul 2018 09:22:16 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:44474 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932746AbeGHNWQ (ORCPT ); Sun, 8 Jul 2018 09:22:16 -0400 Received: from localhost (unknown [46.44.180.42]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 56AB4C87; Sun, 8 Jul 2018 13:22:15 +0000 (UTC) Date: Sun, 8 Jul 2018 15:22:13 +0200 From: Greg Kroah-Hartman To: Javier Martinez Canillas Cc: linux-kernel@vger.kernel.org, Tomeu Vizoso , Rob Herring , Mark Brown , Andy Shevchenko , Peter Robinson , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3] driver core: add a debugfs entry to show deferred devices Message-ID: <20180708132213.GA29000@kroah.com> References: <20180708003256.15655-1-javierm@redhat.com> <20180708132107.GA25491@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180708132107.GA25491@kroah.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 08, 2018 at 03:21:07PM +0200, Greg Kroah-Hartman wrote: > On Sun, Jul 08, 2018 at 02:32:56AM +0200, Javier Martinez Canillas wrote: > > With Device Trees (DT), the dependencies of the devices are defined in the > > DT, then the drivers parse that information to lookup the needed resources > > that have as dependencies. > > > > Since drivers and devices are registered in a non-deterministic way, it is > > possible that a device that is a dependency has not been registered yet by > > the time that is looked up. > > > > In this case the driver that requires this dependency cannot probe and has > > to defer it. So the driver core adds it to a list of deferred devices that > > is iterated again every time that a new driver is probed successfully. > > > > For debugging purposes it may be useful to know what are the devices whose > > probe function was deferred. Add a debugfs entry showing that information. > > > > $ cat /sys/kernel/debug/devices_deferred > > 48070000.i2c:twl@48:bci > > musb-hdrc.0.auto > > omapdrm.0 > > > > This information could be obtained partially by enabling debugging, but it > > means that the kernel log has to be parsed and the probe deferral balanced > > with the successes. This can be error probe and has to be done in a ad-hoc > > manner by everyone who needs to debug these kind of issues. > > > > Since the information is already known by the kernel, just show it to make > > it easier to debug. > > > > Signed-off-by: Javier Martinez Canillas > > Reviewed-by: Andy Shevchenko > > Reviewed-by: Mark Brown > > > > --- > > > > Changes since RFC v1: > > - Remove unneeded ret variable from deferred_devs_show() > > > > Changes since RFC v2: > > - Use DEFINE_SHOW_ATTRIBUTE() macro. > > - Don't propagate debugfs_create_file() error. > > - Remove IS_ENABLED(CONFIG_DEBUG_FS) guards. > > - Drop RFC prefix. > > > > Changes since v1: > > - Better explain in the commit message why this patch is useful. > > - Rename deferred_devices entry to devices_deferred. > > - Add an exit function and remove the debugfs entry. > > > > Changes since v2: > > - Add Andy Shevchenko and Mark Brown Reviewed-by tag. > > - Rebase on top of Greg's driver-core-next branch. > > > > > > drivers/base/dd.c | 30 ++++++++++++++++++++++++++++++ > > 1 file changed, 30 insertions(+) > > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > > index 6ea9c5cece7..140f534ee9c 100644 > > --- a/drivers/base/dd.c > > +++ b/drivers/base/dd.c > > @@ -16,6 +16,7 @@ > > * Copyright (c) 2007-2009 Novell Inc. > > */ > > > > +#include > > #include > > #include > > #include > > @@ -53,6 +54,8 @@ static DEFINE_MUTEX(deferred_probe_mutex); > > static LIST_HEAD(deferred_probe_pending_list); > > static LIST_HEAD(deferred_probe_active_list); > > static atomic_t deferred_trigger_count = ATOMIC_INIT(0); > > +static struct dentry *deferred_devices; > > +static bool initcalls_done; > > Wait, why add this variable? No one uses it that I can see in this > patch, doesn't it create a build warning? > > You did test-build this, right? I just tested it, it causes a build warning, which implies that you did not test this :( greg k-h