linux-kernel - Re: [PATCH v5 1/3] thermal/acpi: Add ACPI trip point routines

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Date:   Fri, 20 Jan 2023 19:27:50 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     srinivas.pandruvada@...ux.intel.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        rui.zhang@...el.com, christophe.jaillet@...adoo.fr
Subject: Re: [PATCH v5 1/3] thermal/acpi: Add ACPI trip point routines

On 20/01/2023 19:15, Rafael J. Wysocki wrote:
> On Fri, Jan 20, 2023 at 7:08 PM Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>>
>>
>> Hi Rafael,
>>
>>
>> On 19/01/2023 14:15, Rafael J. Wysocki wrote:
>>
>> [ ... ]
>>
>>>> +static int thermal_acpi_get_temperature_object(struct acpi_device *adev,
>>>> +                                              char *object, int *temperature)
>>>
>>> So this would become thermal_acpi_get_temp_object(). or even
>>> thermal_acpi_get_temp() because it really returns the temperature
>>> value.
>>>
>>> I also don't particularly like returning values via pointers, which is
>>> entirely avoidable here, because the temperature value obtained from
>>> the ACPI control methods must be a positive number.
>>>
>>> So I would make it
>>>
>>> static int thermal_acpi_get_temp(struct acpi_device *adev, char *object_name)
>>> {
>>
>> We are converting decikelvin -> millicelsius. Even it is very unlikely,
>> the result could be less than zero (eg. -1°C). We won't be able to
>> differentiate -ENODATA with a negative value, no ?
>>
>> In the future, it is possible we will have to deal with cold trip points
>> in order to warm a board. May be we should don't care for now ?
> 
> My point is that the ACPI specification mandates that the return
> values be in deciK and so always non-negative.

I understand that but the code does:

static int thermal_acpi_get_temp(struct acpi_device *adev, char 
*object_name)
{
	...

	return deci_kelvin_to_millicelsius(temp);
}

All the callers do:

...

         ret = thermal_acpi_get_temp(adev, name);
         if (ret < 0)
		return ret;
	/* This could be an error
	 * or negative millicelsius temperature
	 */

	/* here we already have millicelsius */
         trip->temperature = ret;
...

So I guess we want to do:

...

         ret = thermal_acpi_get_temp(adev, name);
         if (ret < 0)
		return ret;

	/* we convert here instead in thermal_acpi_get_temp() */
         trip->temperature = deci_kelvin_to_millicelsius(ret);
...

Sounds good ?


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