[PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev_update()

[PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev_update()

[Daniel Lezcano]

The function thermal_cdev_upadte is called from the throttling
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@linaro.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);
 	}
 
 	return 0;
-- 
2.17.1

Re: [PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev_update()

[Guenter Roeck]

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@linaro.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;
> 

Re: [PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev_update()

[Daniel Lezcano]

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@linaro.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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Re: [PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev_update()

[Guenter Roeck]

On 4/11/20 9:45 AM, Daniel Lezcano wrote:
> 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@linaro.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.
> 
Good question. The author might know/recall. Maybe the idea was that
thermal would update the state to a lower state shortly thereafter.

> 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?
> 
I don't know. I am not exactly familiar with thermal subsystem
particulars. I do recall seeing similar code in other drivers, though.

Either case, your patch does change functionality, and we should not
do that without understanding its impact.

Thanks
Guenter

Re: [PATCH 1/6] thermal: hwmon: Replace the call the thermal_cdev_update()

[Daniel Lezcano]

On 11/04/2020 19:26, Guenter Roeck wrote:
> On 4/11/20 9:45 AM, Daniel Lezcano wrote:
>> 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@linaro.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.
>>
> Good question. The author might know/recall. Maybe the idea was that
> thermal would update the state to a lower state shortly thereafter.
> 
>> 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?
>>
> I don't know. I am not exactly familiar with thermal subsystem
> particulars. I do recall seeing similar code in other drivers, though.

This call is done only in the governors actually.

> Either case, your patch does change functionality, and we should not
> do that without understanding its impact.

Right, so I've been hacking my board, added a pwm-fan and binded the
thermal zone to it.

As expected, the call to thermal_cdev_update() is not needed.

ctx->pwm_fan_state = ctx->pwm_fan_max_state;

intializes to a max value (in my case it is 3). Right after it calls
thermal_cdev_update() which fails to find any instance active because we
are at init time and then calls set_cur_state with the target state set
to zero and passing through a stats usage for nothing.

The ctx->pwm_fan_state is only used by the cooling device ops, so I
don't see any reason why it is set to pwm_fan_max_state before the
compilation condition.

May be there is something subtle here.

Lukasz ? Is there any reason why thermal_cdev_update() was called here ?

IMO, this function is a governor thing and it must be removed from the
cooling device.



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