linux-kernel - Re: [PATCH v2 3/4] thermal: Added Bang-bang thermal governor

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Message-ID: <20140430090108.GC2934@e102654-lin.cambridge.arm.com>
Date:	Wed, 30 Apr 2014 10:01:08 +0100
From:	Javi Merino <javi.merino@....com>
To:	Peter Feuerer <peter@...e.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>, Andreas Mohr <andi@...as.de>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v2 3/4] thermal: Added Bang-bang thermal governor

Hi Peter,

On Tue, Apr 29, 2014 at 10:31:42PM +0100, Peter Feuerer wrote:
> Peter Feuerer writes:
> 
> > Javi Merino writes:
> [...]
> 
> >>> diff --git a/drivers/thermal/gov_bang_bang.c b/drivers/thermal/gov_bang_bang.c
> >>> new file mode 100644
> >>> index 0000000..328dde0
> >>> --- /dev/null
> >>> +++ b/drivers/thermal/gov_bang_bang.c
> >>> @@ -0,0 +1,124 @@
> >>> +/*
> >>> + *  gov_bang_bang.c - A simple thermal throttling governor using hysteresis
> >>> + *
> >>> + *  Copyright (C) 2014 Peter Feuerer <peter@...e.net>
> >>> + *
> >>> + *  Based on step_wise.c with following Copyrights:
> >>> + *  Copyright (C) 2012 Intel Corp
> >>> + *  Copyright (C) 2012 Durgadoss R <durgadoss.r@...el.com>
> >>> + *
> >>> + *
> >>> + * This program is free software; you can redistribute it and/or modify
> >>> + * it under the terms of the GNU General Public License as published by
> >>> + * the Free Software Foundation, version 2.
> >>> + *
> >>> + * This program is distributed in the hope that it will be useful,
> >>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
> >>> + * the GNU General Public License for more details.
> >>> + *
> >>> + */
> >>> +
> >>> +#include <linux/thermal.h>
> >>> +
> >>> +#include "thermal_core.h"
> >>> +
> >>> +static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
> >>> +{
> >>> +	long trip_temp;
> >>> +	unsigned long trip_hyst;
> >>> +	struct thermal_instance *instance;
> >>> +
> >>> +	tz->ops->get_trip_temp(tz, trip, &trip_temp);
> >>> +	tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
> >>> +
> >>> +	dev_dbg(&tz->device, "Trip%d[temp=%ld]:temp=%d:hyst=%ld\n",
> >>> +				trip, trip_temp, tz->temperature,
> >>> +				trip_hyst);
> >>> +
> >>> +	mutex_lock(&tz->lock);
> >>> +
> >>> +	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> >>> +		if (instance->trip != trip)
> >>> +			continue;
> >>> +
> >>> +		/* in case fan is neither on nor off set the fan to active */
> >>> +		if (instance->target != 0 && instance->target != 1)
> >>> +			instance->target = 1;
> >> 
> >> I think you should add a pr_warn() here to warn the user that the
> >> governor is being used with a cooling device that seems to support
> >> more than one cooling state.
> > 
> > Strange thing is, that the first time it is actually called with acerhdf 
> > attached, it comes in with instance→target = -1 … I did not yet find out, 
> > why.
> > 
> > I'll further investigate on this and add some warning to it.
> 
> I found out, that the default init state of a cooling device is:
> 
> drivers/thermal/thermal_core.c:
>  960         dev->target = THERMAL_NO_TARGET;
> 
> While drivers/thermal/thermal_core.h:
>  30 /* Initial state of a cooling device during binding */
>  31 #define THERMAL_NO_TARGET -1UL
> 
> 
> So I changed my patch to this:
> 
> +               /* in case fan is in initial state, switch the fan off */
> +               if (instance->target == THERMAL_NO_TARGET)
> +                       instance->target = 0;
> +
> +               /* in case fan is neither on nor off set the fan to active */
> +               if (instance->target != 0 && instance->target != 1) {
> +                       pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
> +                                       instance->name, instance->target);
> +                       instance->target = 1;
> +               }

That sounds like a better solution, thanks!
Javi

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