linux-kernel - Re: [PATCH v1] thermal: gov_bang_bang: Adjust states of all uninitialized instances

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Message-ID: <71e26995-0438-4868-a96c-3c2f4c9f51e7@arm.com>
Date: Thu, 5 Sep 2024 09:33:14 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>,
 LKML <linux-kernel@...r.kernel.org>, Zhang Rui <rui.zhang@...el.com>,
 Peter Kästle <peter@...e.net>,
 Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v1] thermal: gov_bang_bang: Adjust states of all
 uninitialized instances



On 8/26/24 17:23, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If a cooling device is registered after a thermal zone it should be
> bound to and the trip point it should be bound to has already been
> crossed by the zone temperature on the way up, the cooling device's
> state may need to be adjusted, but the Bang-bang governor will not
> do that because its .manage() callback only looks at thermal instances
> for trip points whose thresholds are below or at the zone temperature.
> 
> Address this by updating bang_bang_manage() to look at all of the
> uninitialized thermal instances and setting their target states in
> accordance with the position of the zone temperature with respect to
> the threshold of the given trip point.
> 
> Fixes: 5f64b4a1ab1b ("thermal: gov_bang_bang: Add .manage() callback")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> Found by code inspection while considering a related change.
> 
> I don't thik it is super-urgent, but it qualifies as 6.12 material IMV.
> 
> ---
>   drivers/thermal/gov_bang_bang.c |   14 ++++++--------
>   1 file changed, 6 insertions(+), 8 deletions(-)
> 
> 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
> @@ -92,23 +92,21 @@ static void bang_bang_manage(struct ther
>   
>   	for_each_trip_desc(tz, td) {
>   		const struct thermal_trip *trip = &td->trip;
> +		bool turn_on;
>   
> -		if (tz->temperature >= td->threshold ||
> -		    trip->temperature == THERMAL_TEMP_INVALID ||
> +		if (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.
> +		 * Adjust the target states for uninitialized thermal instances
> +		 * to the thermal zone temperature and the trip point threshold.
>   		 */
> +		turn_on = tz->temperature >= td->threshold;
>   		list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
>   			if (!instance->initialized && instance->trip == trip)
> -				bang_bang_set_instance_target(instance, 0);
> +				bang_bang_set_instance_target(instance, turn_on);
>   		}
>   	}
>   
> 
> 
> 

That makes sense.

Reviewed-by: Lukasz Luba <lukasz.luba@....com>