From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751677AbbFXIeF (ORCPT ); Wed, 24 Jun 2015 04:34:05 -0400 Received: from mail-qg0-f46.google.com ([209.85.192.46]:33524 "EHLO mail-qg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751247AbbFXId4 (ORCPT ); Wed, 24 Jun 2015 04:33:56 -0400 MIME-Version: 1.0 In-Reply-To: References: <1434622954-26747-3-git-send-email-geert+renesas@glider.be> <1434958282-27376-1-git-send-email-geert+renesas@glider.be> Date: Wed, 24 Jun 2015 10:33:54 +0200 Message-ID: Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code From: Ulf Hansson To: Geert Uytterhoeven Cc: Geert Uytterhoeven , Daniel Lezcano , Thomas Gleixner , "Rafael J. Wysocki" , Kevin Hilman , Magnus Damm , Laurent Pinchart , "linux-pm@vger.kernel.org" , Linux-sh list , "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 [...] >>> >>> @@ -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? Kind regards Uffe From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ulf Hansson Date: Wed, 24 Jun 2015 08:33:54 +0000 Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code Message-Id: 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 [...] >>> >>> @@ -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? Kind regards Uffe