Re: [PATCH v3 3/6] thermal: Added Bang-bang thermal governor

[Peter Feuerer]

Borislav Petkov writes:

> On Sat, May 03, 2014 at 07:59:23PM +0200, Peter Feuerer wrote:
> > The bang-bang thermal governor uses a hysteresis to switch abruptly on
> > or off a cooling device.  It is intended to control fans, which can
> > not be throttled but just switched on or off.
> > Bang-bang cannot be set as default governor as it is intended for
> > special devices only.  For those special devices the driver needs to
> > explicitely request it.
> >
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
> > Cc: Andreas Mohr <andi@xxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxx>
> > Cc: Javi Merino <javi.merino@xxxxxxx>
> > Signed-off-by: Peter Feuerer <peter@xxxxxxxx>
>
> ...
>
> > +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 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) {
>
> ->target is unsigned long so
>
> 		if (instance->target > 1)

Right, but I wanted to clearly point out the two possible states.


> (and btw, a whole unsigned long for a cooling state... 2^64-1 cooling
> states, nice).

Hehe, true, maybe u8 makes more sense, so the compiler can take the action to align it accordingly to prevent bit shifting.

> > +			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
> > +					instance->name, instance->target);
> > +			instance->target = 1;
> > +		}
>
> Can that even happen?

It should not, but if so, we have a warning and I have the feeling we should 
keep it there.

--
--peter;
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