linux-kernel - Re: [PATCH v1 3/4] thermal: gov_bang

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Message-ID: <e03ddc4e-b209-4cfc-bf98-625d03340550@gmail.com>
Date: Tue, 13 Aug 2024 23:04:01 +0200
From: Peter Kästle <xypiie@...il.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Peter Kästle <peter@...e.net>
Subject: Re: [PATCH v1 3/4] thermal: gov_bang_bang: Add .manage() callback

On 13.08.24 16:27, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> After recent changes, the Bang-bang governor may not adjust the
> initial configuration of cooling devices to the actual situation.
> 
> Namely, if a cooling device bound to a certain trip point starts in
> the "on" state and the thermal zone temperature is below the threshold
> of that trip point, the trip point may never be crossed on the way up
> in which case the state of the cooling device will never be adjusted
> because the thermal core will never invoke the governor's
> .trip_crossed() callback.  [Note that there is no issue if the zone
> temperature is at the trip threshold or above it to start with because
> .trip_crossed() will be invoked then to indicate the start of thermal
> mitigation for the given trip.]
> 
> To address this, add a .manage() callback to the Bang-bang governor
> and use it to ensure that all of the thermal instances managed by the
> governor have been initialized properly and the states of all of the
> cooling devices involved have been adjusted to the current zone
> temperature as appropriate.
> 
> Fixes: 530c932bdf75 ("thermal: gov_bang_bang: Use .trip_crossed() instead of .throttle()")
> Link: https://lore.kernel.org/linux-pm/1bfbbae5-42b0-4c7d-9544-e98855715294@piie.net/
> Cc: 6.10+ <stable@...r.kernel.org> # 6.10+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Acked-by: Peter Kästle <peter@...e.net>

> ---
>   drivers/thermal/gov_bang_bang.c |   30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
> 
> Index: linux-pm/drivers/thermal/gov_bang_bang.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/gov_bang_bang.c
> +++ linux-pm/drivers/thermal/gov_bang_bang.c
> @@ -26,6 +26,7 @@ static void bang_bang_set_instance_targe
>   	 * when the trip is crossed on the way down.
>   	 */
>   	instance->target = target;
> +	instance->initialized = true;
>   
>   	dev_dbg(&instance->cdev->device, "target=%ld\n", instance->target);
>   
> @@ -80,8 +81,37 @@ static void bang_bang_control(struct the
>   	}
>   }
>   
> +static void bang_bang_manage(struct thermal_zone_device *tz)
> +{
> +	const struct thermal_trip_desc *td;
> +	struct thermal_instance *instance;
> +
> +	for_each_trip_desc(tz, td) {
> +		const struct thermal_trip *trip = &td->trip;
> +
> +		if (tz->temperature >= td->threshold ||
> +		    trip->temperature == THERMAL_TEMP_INVALID ||
> +		    trip->type == THERMAL_TRIP_CRITICAL ||
> +		    trip->type == THERMAL_TRIP_HOT)
> +			continue;
> +
> +		/*
> +		 * If the initial cooling device state is "on", but the zone
> +		 * temperature is not above the trip point, the core will not
> +		 * call bang_bang_control() until the zone temperature reaches
> +		 * the trip point temperature which may be never.  In those
> +		 * cases, set the initial state of the cooling device to 0.
> +		 */
> +		list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> +			if (!instance->initialized && instance->trip == trip)
> +				bang_bang_set_instance_target(instance, 0);
> +		}
> +	}
> +}
> +
>   static struct thermal_governor thermal_gov_bang_bang = {
>   	.name		= "bang_bang",
>   	.trip_crossed	= bang_bang_control,
> +	.manage		= bang_bang_manage,
>   };
>   THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
> 
> 
>