linux-kernel - Re: [PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev

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Message-ID: <4ded7975-499d-024a-283f-de4f82d295f3@roeck-us.net>
Date:   Fri, 10 Apr 2020 18:32:42 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>, rui.zhang@...el.com
Cc:     amit.kucheria@...durent.com, linux-kernel@...r.kernel.org,
        Kamil Debski <kamil@...as.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jean Delvare <jdelvare@...e.com>,
        "open list:PWM FAN DRIVER" <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH 1/6] thermal: hwmon: Replace the call the
 thermal_cdev_update()

On 4/10/20 3:12 PM, Daniel Lezcano wrote:
> The function thermal_cdev_upadte is called from the throttling

misspelled

> functions in the governors not from the cooling device itself.
> 
> The cooling device is set to its maximum state and then updated. Even
> if I don't get the purpose of probing the pwm-fan to its maximum
> cooling state, we can replace the thermal_cdev_update() call to the
> internal set_cur_state() function directly.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  drivers/hwmon/pwm-fan.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 30b7b3ea8836..a654ecdf21ab 100644
> --- a/drivers/hwmon/pwm-fan.c
> +++ b/drivers/hwmon/pwm-fan.c
> @@ -372,7 +372,6 @@ static int pwm_fan_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>  
> -	ctx->pwm_fan_state = ctx->pwm_fan_max_state;
>  	if (IS_ENABLED(CONFIG_THERMAL)) {
>  		cdev = devm_thermal_of_cooling_device_register(dev,
>  			dev->of_node, "pwm-fan", ctx, &pwm_fan_cooling_ops);
> @@ -384,7 +383,7 @@ static int pwm_fan_probe(struct platform_device *pdev)
>  			return ret;
>  		}
>  		ctx->cdev = cdev;
> -		thermal_cdev_update(cdev);
> +		pwm_fan_set_cur_state(cdev, ctx->pwm_fan_max_state);

So far the function would only change the state if the new
state is not equal to the old state. This was the case because
pwm_fan_state was set to pwm_fan_max_state, and the call to
thermal_cdev_update() and thus pwm_fan_set_cur_state() would
do nothing except update statistics. The old code _assumed_
that the current state is pwm_fan_max_state. The new code
enforces it. That is a substantial semantic change, and it
is not really reflected in the commit message. Is that really
what you want ? If so, the commit message needs to state that
and explain the rationale.

Thanks,
Guenter

>  	}
>  
>  	return 0;
>