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

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Message-ID: <907914e7-7f5a-e66d-bf38-be110aa1f6f0@linaro.org>
Date:   Sat, 11 Apr 2020 18:45:59 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Guenter Roeck <linux@...ck-us.net>, 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 11/04/2020 03:32, Guenter Roeck wrote:
> 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.

Well, to be honest I'm not getting the rational of calling
thermal_cdev_update(cdev) right after
devm_thermal_of_cooling_device_register() neither setting pwm_fan_state
to pwm_fan_max_state.

Do we have the guarantee there is at this point a thermal instance
making the target state working when thermal_cdev_update is called?

Are we sure a thermal_cdev_update(cdev) is actually right here?


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