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

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Message-ID: <3d67c7d9a0f4aec1c2f9836abc95abdd8a20fe56.camel@intel.com>
Date: Fri, 16 Aug 2024 03:00:13 +0000
From: "Zhang, Rui" <rui.zhang@...el.com>
To: "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, "rjw@...ysocki.net"
	<rjw@...ysocki.net>
CC: "lukasz.luba@....com" <lukasz.luba@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>, "peter@...e.net"
	<peter@...e.net>
Subject: Re: [PATCH v1 3/4] thermal: gov_bang_bang: Add .manage() callback

On Tue, 2024-08-13 at 16:27 +0200, 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>

Reviewed-by: Zhang Rui <rui.zhang@...el.com>

thanks,
rui

> ---
>  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(instanc
> e, 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);
> 
> 
>