From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753496AbbFXNWK (ORCPT ); Wed, 24 Jun 2015 09:22:10 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:60843 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752536AbbFXNWE (ORCPT ); Wed, 24 Jun 2015 09:22:04 -0400 From: "Rafael J. Wysocki" To: Geert Uytterhoeven Cc: Ulf Hansson , Geert Uytterhoeven , Daniel Lezcano , Thomas Gleixner , Kevin Hilman , Magnus Damm , Laurent Pinchart , "linux-pm@vger.kernel.org" , Linux-sh list , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code Date: Wed, 24 Jun 2015 15:48:12 +0200 Message-ID: <1472640.FZpH0ugFKI@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> 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 On Wednesday, June 24, 2015 10:35:44 AM Geert Uytterhoeven wrote: > On Wed, Jun 24, 2015 at 10:33 AM, Ulf Hansson wrote: > > [...] > > > >>>> > >>>> @@ -2183,6 +2191,7 @@ int genpd_dev_pm_attach(struct device *dev) > >>>> { > >>>> struct of_phandle_args pd_args; > >>>> struct generic_pm_domain *pd; > >>>> + unsigned int i; > >>>> int ret; > >>>> > >>>> if (!dev->of_node) > >>>> @@ -2218,10 +2227,13 @@ int genpd_dev_pm_attach(struct device *dev) > >>>> > >>>> dev_dbg(dev, "adding to PM domain %s\n", pd->name); > >>>> > >>>> - while (1) { > >>>> + for (i = 0; i < GENPD_RETRIES; i++) { > >>>> ret = pm_genpd_add_device(pd, dev); > >>>> if (ret != -EAGAIN) > >>>> break; > >>>> + > >>>> + if (i > GENPD_RETRIES / 2) > >>>> + udelay(GENPD_DELAY_US); > >>> > >>> In this execution path, we retry when getting -EAGAIN while believing > >>> the reason to the error are only *temporary* as we are soon waiting > >>> for all devices in the genpd to be system PM resumed. At least that's > >>> my understanding to why we want to deal with -EAGAIN here, but I might > >>> be wrong. > >>> > >>> In this regards, I wonder whether it could be better to re-try only a > >>> few times but with a far longer interval time than a couple us. What > >>> do you think? > >> > >> That's indeed viable. I have no idea for how long this temporary state can > >> extend. > > > > That will depend on the system PM resume time for the devices residing > > in the genpd. So, I guess we need a guestimate then. How about a total > > sleep time of a few seconds? > > > >> > >>> However, what if the reason to why we get -EAGAIN isn't *temporary*, > >>> because we are about to enter system PM suspend state. Then the caller > >>> of this function which comes via some bus' ->probe(), will hang until > >>> the a system PM resume is completed. Is that really going to work? So, > >>> for this case your limited re-try approach will affect this scenario > >>> as well, have you considered that? > >> > >> There's a limit on the number of retries, so it won't hang indefinitely. > > > > What happens with the timer functions (like msleep()) during the > > system PM suspend transition? > > I guess we can no longer call msleep() after syscore suspend? That's correct. Time is effectively frozen at that point. Rafael From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Date: Wed, 24 Jun 2015 13:48:12 +0000 Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code Message-Id: <1472640.FZpH0ugFKI@vostro.rjw.lan> List-Id: References: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> In-Reply-To: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sh@vger.kernel.org On Wednesday, June 24, 2015 10:35:44 AM Geert Uytterhoeven wrote: > On Wed, Jun 24, 2015 at 10:33 AM, Ulf Hansson wrote: > > [...] > > > >>>> > >>>> @@ -2183,6 +2191,7 @@ int genpd_dev_pm_attach(struct device *dev) > >>>> { > >>>> struct of_phandle_args pd_args; > >>>> struct generic_pm_domain *pd; > >>>> + unsigned int i; > >>>> int ret; > >>>> > >>>> if (!dev->of_node) > >>>> @@ -2218,10 +2227,13 @@ int genpd_dev_pm_attach(struct device *dev) > >>>> > >>>> dev_dbg(dev, "adding to PM domain %s\n", pd->name); > >>>> > >>>> - while (1) { > >>>> + for (i = 0; i < GENPD_RETRIES; i++) { > >>>> ret = pm_genpd_add_device(pd, dev); > >>>> if (ret != -EAGAIN) > >>>> break; > >>>> + > >>>> + if (i > GENPD_RETRIES / 2) > >>>> + udelay(GENPD_DELAY_US); > >>> > >>> In this execution path, we retry when getting -EAGAIN while believing > >>> the reason to the error are only *temporary* as we are soon waiting > >>> for all devices in the genpd to be system PM resumed. At least that's > >>> my understanding to why we want to deal with -EAGAIN here, but I might > >>> be wrong. > >>> > >>> In this regards, I wonder whether it could be better to re-try only a > >>> few times but with a far longer interval time than a couple us. What > >>> do you think? > >> > >> That's indeed viable. I have no idea for how long this temporary state can > >> extend. > > > > That will depend on the system PM resume time for the devices residing > > in the genpd. So, I guess we need a guestimate then. How about a total > > sleep time of a few seconds? > > > >> > >>> However, what if the reason to why we get -EAGAIN isn't *temporary*, > >>> because we are about to enter system PM suspend state. Then the caller > >>> of this function which comes via some bus' ->probe(), will hang until > >>> the a system PM resume is completed. Is that really going to work? So, > >>> for this case your limited re-try approach will affect this scenario > >>> as well, have you considered that? > >> > >> There's a limit on the number of retries, so it won't hang indefinitely. > > > > What happens with the timer functions (like msleep()) during the > > system PM suspend transition? > > I guess we can no longer call msleep() after syscore suspend? That's correct. Time is effectively frozen at that point. Rafael