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Date:   Mon, 11 Jan 2021 18:13:29 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>, rui.zhang@...el.com
Cc:     mjg59@...on.org.uk, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, amitk@...nel.org,
        Jonathan Corbet <corbet@....net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 1/6] thermal/core: Remove the 'forced_passive' option



On 12/14/20 6:38 PM, Daniel Lezcano wrote:
> The code was reorganized in 2012 with the commit 0c01ebbfd3caf1.
> 
> The main change is a loop on the trip points array and a unconditional
> call to the throttle() ops of the governors for each of them even if
> the trip temperature is not reached yet.
> 
> With this change, the 'forced_passive' is no longer checked in the
> thermal_zone_device_update() function but in the step wise governor's
> throttle() callback.
> 
> As the force_passive does no belong to the trip point array, the
> thermal_zone_device_update() can not compare with the specified
> passive temperature, thus does not detect the passive limit has been
> crossed. Consequently, throttle() is never called and the
> 'forced_passive' branch is unreached.
> 
> In addition, the default processor cooling device is not automatically
> bound to the thermal zone if there is not passive trip point, thus the
> 'forced_passive' can not operate.
> 
> If there is an active trip point, then the throttle function will be
> called to mitigate at this temperature and the 'forced_passive' will
> override the mitigation of the active trip point in this case but with
> the default cooling device bound to the thermal zone, so usually a
> fan, and that is not a passive cooling effect.
> 
> Given the regression exists since more than 8 years, nobody complained
> and at the best of my knowledge there is no bug open in
> https://bugzilla.kernel.org, it is reasonable to say it is unused.
> 
> Remove the 'forced_passive' related code.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Reviewed-by: Thara Gopinath <thara.gopinath@...aro.org>

> ---
>   .../driver-api/thermal/sysfs-api.rst          | 13 ---
>   drivers/thermal/gov_step_wise.c               | 14 +---
>   drivers/thermal/thermal_sysfs.c               | 80 -------------------
>   include/linux/thermal.h                       |  4 -
>   4 files changed, 3 insertions(+), 108 deletions(-)
> 
> diff --git a/Documentation/driver-api/thermal/sysfs-api.rst b/Documentation/driver-api/thermal/sysfs-api.rst
> index e7520cb439ac..a4969c474cc3 100644
> --- a/Documentation/driver-api/thermal/sysfs-api.rst
> +++ b/Documentation/driver-api/thermal/sysfs-api.rst
> @@ -520,19 +520,6 @@ available_policies
>   
>   	RW, Optional
>   
> -passive
> -	Attribute is only present for zones in which the passive cooling
> -	policy is not supported by native thermal driver. Default is zero
> -	and can be set to a temperature (in millidegrees) to enable a
> -	passive trip point for the zone. Activation is done by polling with
> -	an interval of 1 second.
> -
> -	Unit: millidegrees Celsius
> -
> -	Valid values: 0 (disabled) or greater than 1000
> -
> -	RW, Optional
> -
>   emul_temp
>   	Interface to set the emulated temperature method in thermal zone
>   	(sensor). After setting this temperature, the thermal zone may pass
> diff --git a/drivers/thermal/gov_step_wise.c b/drivers/thermal/gov_step_wise.c
> index 2ae7198d3067..12acb12aac50 100644
> --- a/drivers/thermal/gov_step_wise.c
> +++ b/drivers/thermal/gov_step_wise.c
> @@ -109,7 +109,7 @@ static void update_passive_instance(struct thermal_zone_device *tz,
>   	 * If value is +1, activate a passive instance.
>   	 * If value is -1, deactivate a passive instance.
>   	 */
> -	if (type == THERMAL_TRIP_PASSIVE || type == THERMAL_TRIPS_NONE)
> +	if (type == THERMAL_TRIP_PASSIVE)
>   		tz->passive += value;
>   }
>   
> @@ -122,13 +122,8 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
>   	bool throttle = false;
>   	int old_target;
>   
> -	if (trip == THERMAL_TRIPS_NONE) {
> -		trip_temp = tz->forced_passive;
> -		trip_type = THERMAL_TRIPS_NONE;
> -	} else {
> -		tz->ops->get_trip_temp(tz, trip, &trip_temp);
> -		tz->ops->get_trip_type(tz, trip, &trip_type);
> -	}
> +	tz->ops->get_trip_temp(tz, trip, &trip_temp);
> +	tz->ops->get_trip_type(tz, trip, &trip_type);
>   
>   	trend = get_tz_trend(tz, trip);
>   
> @@ -189,9 +184,6 @@ static int step_wise_throttle(struct thermal_zone_device *tz, int trip)
>   
>   	thermal_zone_trip_update(tz, trip);
>   
> -	if (tz->forced_passive)
> -		thermal_zone_trip_update(tz, THERMAL_TRIPS_NONE);
> -
>   	mutex_lock(&tz->lock);
>   
>   	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index 0866e949339b..4e7f9e880d76 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -216,49 +216,6 @@ trip_point_hyst_show(struct device *dev, struct device_attribute *attr,
>   	return ret ? ret : sprintf(buf, "%d\n", temperature);
>   }
>   
> -static ssize_t
> -passive_store(struct device *dev, struct device_attribute *attr,
> -	      const char *buf, size_t count)
> -{
> -	struct thermal_zone_device *tz = to_thermal_zone(dev);
> -	int state;
> -
> -	if (sscanf(buf, "%d\n", &state) != 1)
> -		return -EINVAL;
> -
> -	/* sanity check: values below 1000 millicelcius don't make sense
> -	 * and can cause the system to go into a thermal heart attack
> -	 */
> -	if (state && state < 1000)
> -		return -EINVAL;
> -
> -	if (state && !tz->forced_passive) {
> -		if (!tz->passive_delay)
> -			tz->passive_delay = 1000;
> -		thermal_zone_device_rebind_exception(tz, "Processor",
> -						     sizeof("Processor"));
> -	} else if (!state && tz->forced_passive) {
> -		tz->passive_delay = 0;
> -		thermal_zone_device_unbind_exception(tz, "Processor",
> -						     sizeof("Processor"));
> -	}
> -
> -	tz->forced_passive = state;
> -
> -	thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
> -
> -	return count;
> -}
> -
> -static ssize_t
> -passive_show(struct device *dev, struct device_attribute *attr,
> -	     char *buf)
> -{
> -	struct thermal_zone_device *tz = to_thermal_zone(dev);
> -
> -	return sprintf(buf, "%d\n", tz->forced_passive);
> -}
> -
>   static ssize_t
>   policy_store(struct device *dev, struct device_attribute *attr,
>   	     const char *buf, size_t count)
> @@ -403,7 +360,6 @@ static DEVICE_ATTR_RW(sustainable_power);
>   
>   /* These thermal zone device attributes are created based on conditions */
>   static DEVICE_ATTR_RW(mode);
> -static DEVICE_ATTR_RW(passive);
>   
>   /* These attributes are unconditionally added to a thermal zone */
>   static struct attribute *thermal_zone_dev_attrs[] = {
> @@ -438,45 +394,9 @@ static const struct attribute_group thermal_zone_mode_attribute_group = {
>   	.attrs = thermal_zone_mode_attrs,
>   };
>   
> -/* We expose passive only if passive trips are present */
> -static struct attribute *thermal_zone_passive_attrs[] = {
> -	&dev_attr_passive.attr,
> -	NULL,
> -};
> -
> -static umode_t thermal_zone_passive_is_visible(struct kobject *kobj,
> -					       struct attribute *attr,
> -					       int attrno)
> -{
> -	struct device *dev = kobj_to_dev(kobj);
> -	struct thermal_zone_device *tz;
> -	enum thermal_trip_type trip_type;
> -	int count, passive = 0;
> -
> -	tz = container_of(dev, struct thermal_zone_device, device);
> -
> -	for (count = 0; count < tz->trips && !passive; count++) {
> -		tz->ops->get_trip_type(tz, count, &trip_type);
> -
> -		if (trip_type == THERMAL_TRIP_PASSIVE)
> -			passive = 1;
> -	}
> -
> -	if (!passive)
> -		return attr->mode;
> -
> -	return 0;
> -}
> -
> -static const struct attribute_group thermal_zone_passive_attribute_group = {
> -	.attrs = thermal_zone_passive_attrs,
> -	.is_visible = thermal_zone_passive_is_visible,
> -};
> -
>   static const struct attribute_group *thermal_zone_attribute_groups[] = {
>   	&thermal_zone_attribute_group,
>   	&thermal_zone_mode_attribute_group,
> -	&thermal_zone_passive_attribute_group,
>   	/* This is not NULL terminated as we create the group dynamically */
>   };
>   
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index c80032322158..a57232a9a6f9 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -131,9 +131,6 @@ struct thermal_cooling_device {
>   			trip point.
>    * @prev_high_trip:	the above current temperature if you've crossed a
>   			passive trip point.
> - * @forced_passive:	If > 0, temperature at which to switch on all ACPI
> - *			processor cooling devices.  Currently only used by the
> - *			step-wise governor.
>    * @need_update:	if equals 1, thermal_zone_device_update needs to be invoked.
>    * @ops:	operations this &thermal_zone_device supports
>    * @tzp:	thermal zone parameters
> @@ -167,7 +164,6 @@ struct thermal_zone_device {
>   	int passive;
>   	int prev_low_trip;
>   	int prev_high_trip;
> -	unsigned int forced_passive;
>   	atomic_t need_update;
>   	struct thermal_zone_device_ops *ops;
>   	struct thermal_zone_params *tzp;
> 

-- 
Warm Regards
Thara

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