Re: [RESEND PATCH v4 1/5] thermal: Add support for hardware-tracked trip points

[Javi Merino <javi.merino@arm.com>]

Hi Caesar,

On Fri, May 27, 2016 at 04:36:44PM +0800, Caesar Wang wrote:
> From: Sascha Hauer <s.hauer@pengutronix.de>
> 
> 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@kapsi.fi>
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> Signed-off-by: Caesar Wang <wxt@rock-chips.com>
> Cc: Zhang Rui <rui.zhang@intel.com>
> Cc: Eduardo Valentin <edubezval@gmail.com>
> Cc: linux-pm@vger.kernel.org
> 
> ---
> 
> Changes in v4:
> - Missing the lock added in v3.
> 
> Changes in v3:
> - as Javi comments on https://patchwork.kernel.org/patch/9001281/.
> - add the lock for preventing the called from multi placce
> - add the note for pre_low/high_trip.
> 
> Changes in v2:
> - update the sysfs-api.txt for set_trips.
> 
>  Documentation/thermal/sysfs-api.txt |  7 +++++
>  drivers/thermal/thermal_core.c      | 56 +++++++++++++++++++++++++++++++++++++
>  include/linux/thermal.h             |  7 +++++
>  3 files changed, 70 insertions(+)
> 
> diff --git a/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
> index efc3f3d..75d8838 100644
> --- a/Documentation/thermal/sysfs-api.txt
> +++ b/Documentation/thermal/sysfs-api.txt
> @@ -49,6 +49,9 @@ temperature) and throttle appropriate devices.
>  	.bind: bind the thermal zone device with a thermal cooling device.
>  	.unbind: unbind the thermal zone device with a thermal cooling device.
>  	.get_temp: get the current temperature of the thermal zone.
> +	.set_trips: set the trip points window. Whenever the current temperature
> +		    is updated, the trip points immediately below and above the
> +		    current temperature are found.
>  	.get_mode: get the current mode (enabled/disabled) of the thermal zone.
>  	    - "enabled" means the kernel thermal management is enabled.
>  	    - "disabled" will prevent kernel thermal driver action upon trip points
> @@ -95,6 +98,10 @@ temperature) and throttle appropriate devices.
>  			get_temp:	a pointer to a function that reads the
>  					sensor temperature. This is mandatory
>  					callback provided by sensor driver.
> +			set_trips:      a pointer to a function that sets a
> +					temperature window. When this window is
> +					left the driver must inform the thermal
> +					core via thermal_zone_device_update.
>  			get_trend: 	a pointer to a function that reads the
>  					sensor temperature trend.
>  			set_emul_temp:	a pointer to a function that sets
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 5133cd1..0591438 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -520,6 +520,55 @@ exit:
>  }
>  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, ret;
> +
> +	if (!tz->ops->set_trips)
> +		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;

You only use the hysteresis for the low trip point and not for the
high trip point.  Shouldn't you also add:

		trip_high = trip_temp + hysteresis;

...

> +
> +		if (trip_low < temp && trip_low > low)
> +			low = trip_low;
> +
> +		if (trip_temp > temp && trip_temp < high)
> +			high = trip_temp;

... and here:

		if (trip_high > temp && trip_high < high)
			high = trip_high;

> +	}
> +
> +	/* No need to change trip points */
> +	if (tz->prev_low_trip == low && tz->prev_high_trip == high)
> +		return;
> +
> +	mutex_lock(&tz->lock);

I think you should get the lock for the whole function, including the
read of tz->temperature .  I know I said that the lock should be
acquired before the if condition before but thinking about it, I think
there may be a race condition if userspace updates the hysteresis
while thermal_zone_device_update() is updating the temperature: you
could have the cpu that is updating the hysteresis seeing the old
temperature while the cpu that is updating the temperature would see
the old hysteresis.  I think it's safer if this whole function is
protected from the lock, from the read of tz->temperature until the
end.

Cheers,
Javi

> +
> +	tz->prev_low_trip = low;
> +	tz->prev_high_trip = high;
> +
> +	dev_dbg(&tz->device, "new temperature boundaries: %d < x < %d\n",
> +			low, high);
> +
> +	/*
> +	 * Set a temperature window. When this window is left the driver
> +	 * must inform the thermal core via thermal_zone_device_update.
> +	 */
> +	ret = tz->ops->set_trips(tz, low, high);
> +	if (ret)
> +		dev_err(&tz->device, "Failed to set trips: %d\n", ret);
> +
> +	mutex_unlock(&tz->lock);
> +}
> +
>  static void update_temperature(struct thermal_zone_device *tz)
>  {
>  	int temp, ret;
> @@ -569,6 +618,8 @@ void thermal_zone_device_update(struct thermal_zone_device *tz)
>  
>  	update_temperature(tz);
>  
> +	thermal_zone_set_trips(tz);
> +
>  	for (count = 0; count < tz->trips; count++)
>  		handle_thermal_trip(tz, count);
>  }
> @@ -754,6 +805,9 @@ trip_point_hyst_store(struct device *dev, struct device_attribute *attr,
>  	 */
>  	ret = tz->ops->set_trip_hyst(tz, trip, temperature);
>  
> +	if (!ret)
> +		thermal_zone_set_trips(tz);
> +
>  	return ret ? ret : count;
>  }
>