Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753284AbaJFSB1 (ORCPT ); Mon, 6 Oct 2014 14:01:27 -0400 Received: from mail-qa0-f51.google.com ([209.85.216.51]:43714 "EHLO mail-qa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752318AbaJFSBZ (ORCPT ); Mon, 6 Oct 2014 14:01:25 -0400 Date: Mon, 6 Oct 2014 14:01:13 -0400 From: Eduardo Valentin To: Lukasz Majewski Cc: Zhang Rui , Linux PM list , Lukasz Majewski , Bartlomiej Zolnierkiewicz , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] thermal: core: fix: Initialize the max_state variable to 0 Message-ID: <20141006180110.GA5524@developer> References: <1411547232-21493-1-git-send-email-l.majewski@samsung.com> <1411547232-21493-3-git-send-email-l.majewski@samsung.com> <20141002222649.GB11510@developer> <20141003102628.7a8f36f7@amdc2363> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141003102628.7a8f36f7@amdc2363> User-Agent: Mutt/1.5.22 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 03, 2014 at 10:26:28AM +0200, Lukasz Majewski wrote: > Hi Eduardo, > > > Hello Lukasz, > > > > On Wed, Sep 24, 2014 at 10:27:11AM +0200, Lukasz Majewski wrote: > > > Pointer to the uninitialized max_state variable is passed to get the > > > maximal cooling state. > > > For CPU cooling device (cpu_cooling.c) the cpufreq_get_max_state() > > > is called, which even when error occurs will return the max_state > > > variable unchanged. > > > Since error for ->get_max_state() is not checked, the automatically > > > > > > Good that you added a fix in your series for this. > > > > > > > allocated value of max_state is used for (upper > max_state) > > > comparison. For any possible max_state value it is very unlikely > > > that it will be less than upper. > > > As a consequence, the cooling device is bind even without the backed > > > cpufreq table initialized. > > > > > > This initialization will prevent from accidental binding trip > > > points to cpu freq cooling frequencies when cpufreq driver itself > > > is not yet fully initialized. > > > > Although I agree with the fix, as long as we also include a check for > > the .get_max_state return value, I believe the problem you are > > describing is about initialization sequence. > > As you pointed out - the problem here is with initialization sequence. > Thermal and cpufreq cores are initialized very early. > > However, the get_max_state() for cpu_cooling.c device (as it is the > pervasive way of cooling things) accesses cpufreq policy to get the > freq_table and count available states. > > The issue here is with late initialization of cpufreq policy. > > Up till now the cpu_cooling device was bind even when the > get_max_state() returned -EINVAL and everything worked after late > cpufreq policy initialization. However, during this time window the > thermal driver is not configured. > > > > > In general, I believe we need a better > > sequencing between thermal and cpufreq subsystems. One way out is to > > include a check for cpufreq driver in the thermal driver, and return > > -EPROBE_DEFER when cpufreq is not ready. > > I think that we could return -EPROBE_DEFER when cpufreq's policy is not > yet available and subscribe to cpufreq notifier to call > bind_cooling_device then. I agree with this approach, as long as we keep the existing users of cpufreq cooling in a working state. Cheers > > Let's wait for Zhang opinion since he looks after the thermal core code. > > > > > > > > > Signed-off-by: Lukasz Majewski > > > --- > > > drivers/thermal/thermal_core.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/thermal/thermal_core.c > > > b/drivers/thermal/thermal_core.c index 454884a..747618a 100644 > > > --- a/drivers/thermal/thermal_core.c > > > +++ b/drivers/thermal/thermal_core.c > > > @@ -927,7 +927,7 @@ int thermal_zone_bind_cooling_device(struct > > > thermal_zone_device *tz, struct thermal_instance *pos; > > > struct thermal_zone_device *pos1; > > > struct thermal_cooling_device *pos2; > > > - unsigned long max_state; > > > + unsigned long max_state = 0; > > > int result; > > > > > > if (trip >= tz->trips || (trip < 0 && trip != > > > THERMAL_TRIPS_NONE)) -- > > > 2.0.0.rc2 > > > > > > > > > -- > Best regards, > > Lukasz Majewski > > Samsung R&D Institute Poland (SRPOL) | Linux Platform Group -- 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/