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

Peter Feuerer
2014-07-18T16:24:35Z

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@linux-foundation.org>
>> Cc: Zhang Rui <rui.zhang@intel.com>
>> Cc: Andreas Mohr <andi@lisas.de>
>> Cc: Borislav Petkov <bp@suse.de>
>> Cc: Javi Merino <javi.merino@arm.com>
>> Signed-off-by: Peter Feuerer <peter@piie.net>
>
> ...
>
>> +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;