Re: [PATCH 11/15] thermal: thermal: Add support for hardware-tracked trip points

[Mikko Perttunen]

Thanks for picking up this patch :)

Sorry for being late with these, but here's a few comments..

On 05/13/2015 11:52 AM, Sascha Hauer wrote:
> This adds support for hardware-tracked trip points to the device tree
> thermal sensor framework.
>
> The framework supports an arbitrary number of trip points. Whenever
> the current temperature is updated, the trip points immediately
> below and above the current temperature are found. A .set_trips
> callback is then called with the temperatures. If there is no trip
> point above or below the current temperature, the passed trip
> temperature will be -INT_MAX or INT_MAX respectively. In this callback,
> the driver should program the hardware such that it is notified
> when either of these trip points are triggered. When a trip point
> is triggered, the driver should call `thermal_zone_device_update'
> for the respective thermal zone. This will cause the trip points
> to be updated again.
>
> If .set_trips is not implemented, the framework behaves as before.
>
> This patch is based on an earlier version from Mikko Perttunen
> <mikko.perttunen@xxxxxxxx>
>
> Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> ---
>  drivers/thermal/thermal_core.c | 43 
++++++++++++++++++++++++++++++++++++++++++
>  include/linux/thermal.h        |  3 +++
>  2 files changed, 46 insertions(+)
>
> diff --git a/drivers/thermal/thermal_core.c 
b/drivers/thermal/thermal_core.c
> index 6bbf61f..3ae1795 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -453,6 +453,45 @@ int thermal_zone_get_temp(struct 
thermal_zone_device *tz, int *temp)
>  }
>  EXPORT_SYMBOL_GPL(thermal_zone_get_temp);
>
> +static void thermal_zone_set_trips(struct thermal_zone_device *tz)
> +{
> +	int low = -INT_MAX;
> +	int high = INT_MAX;
> +	int trip_temp, hysteresis;
> +	int temp = tz->temperature;
> +	int i;
> +
> +	if (!tz->ops->set_trips)
> +		return;
> +
> +	/* No need to change trip points */
> +	if (temp > tz->prev_low_trip && temp < tz->prev_high_trip)
> +		return;
> +
> +	for (i = 0; i < tz->trips; i++) {
> +		int trip_low;
> +
> +		tz->ops->get_trip_temp(tz, i, &trip_temp);
> +		tz->ops->get_trip_hyst(tz, i, &hysteresis);
> +
> +		trip_low = trip_temp - hysteresis;
> +
> +		if (trip_low < temp && trip_low > low)
> +			low = trip_low;
> +
> +		if (trip_temp > temp && trip_temp < high)
> +			high = trip_temp;
> +	}
> +
> +	tz->prev_low_trip = low;
> +	tz->prev_high_trip = high;
> +
> +	dev_dbg(&tz->device, "new temperature boundaries: %d < x < %d\n",
> +			low, high);
> +
> +	tz->ops->set_trips(tz, low, high);

This should probably do something if set_trips returns an error code; at 
least an error message, perhaps enable polling? I'm not exactly sure 
what safety features the thermal framework has in general if errors happen..

One interesting thing I noticed was that at least the bang-bang governor 
only acts if the temperature is properly smaller than (trip temp - 
hysteresis). So perhaps we should specify the non-tripping range as 
[low, high)? Or we could change bang-bang.

> +}
> +
>  void thermal_zone_device_update(struct thermal_zone_device *tz)
>  {
>  	int temp, ret, count;
> @@ -479,6 +518,8 @@ void thermal_zone_device_update(struct 
thermal_zone_device *tz)
>  	dev_dbg(&tz->device, "last_temperature=%d, current_temperature=%d\n",
>  				tz->last_temperature, tz->temperature);
>
> +	thermal_zone_set_trips(tz);
> +
>  	for (count = 0; count < tz->trips; count++)
>  		handle_thermal_trip(tz, count);
>  }

set_trips should also be called from temp_store and other places that 
modify values that affect the trip points.

> @@ -1494,6 +1535,8 @@ struct thermal_zone_device 
*thermal_zone_device_register(const char *type,
>  	tz->trips = trips;
>  	tz->passive_delay = passive_delay;
>  	tz->polling_delay = polling_delay;
> +	tz->prev_low_trip = INT_MAX;
> +	tz->prev_high_trip = -INT_MAX;
>
>  	dev_set_name(&tz->device, "thermal_zone%d", tz->id);
>  	result = device_register(&tz->device);
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index 07bd5e8..aef6e13 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -87,6 +87,7 @@ struct thermal_zone_device_ops {
>  	int (*unbind) (struct thermal_zone_device *,
>  		       struct thermal_cooling_device *);
>  	int (*get_temp) (struct thermal_zone_device *, int *);
> +	int (*set_trips) (struct thermal_zone_device *, int, int);
>  	int (*get_mode) (struct thermal_zone_device *,
>  			 enum thermal_device_mode *);
>  	int (*set_mode) (struct thermal_zone_device *,
> @@ -180,6 +181,8 @@ struct thermal_zone_device {
>  	int last_temperature;
>  	int emul_temperature;
>  	int passive;
> +	int prev_low_trip;
> +	int prev_high_trip;
>  	unsigned int forced_passive;
>  	const struct thermal_zone_device_ops *ops;
>  	const struct thermal_zone_params *tzp;
>
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