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SubjectRe: [PATCH v3 2/2] ACPI: fan: Add hwmon support
From
Am 12.04.24 um 23:01 schrieb Guenter Roeck:

> On Fri, Apr 12, 2024 at 10:27:56PM +0200, Armin Wolf wrote:
>>>> + case hwmon_fan_fault:
>>>> + *val = (fst.speed == FAN_SPEED_UNAVAILABLE);
>>> Is it documented that this is indeed a fault (broken fan) ?
>>>
>> Hi,
>>
>> it actually means that the fan does not support speed reporting.
>>
>>>> + return 0;
>>>> + default:
>>>> + break;
>>>> + }
>>>> + break;
>>>> + case hwmon_power:
>>>> + fps = acpi_fan_get_current_fps(fan, fst.control);
>>>> + if (!fps)
>>>> + return -ENODATA;
>>>> +
>>>> + switch (attr) {
>>>> + case hwmon_power_input:
>>>> + if (fps->power == FAN_POWER_UNAVAILABLE)
>>>> + return -ENODATA;
>>>> +
>>>> + if (fps->power > LONG_MAX / MICROWATT_PER_MILLIWATT)
>>>> + return -EOVERFLOW;
>>>> +
>>>> + *val = fps->power * MICROWATT_PER_MILLIWATT;
>>>> + return 0;
>>>> + case hwmon_power_fault:
>>>> + *val = (fps->power == FAN_POWER_UNAVAILABLE);
>>> Is it documented that this is indeed a power supply failure ?
>>> What if the value is simply not reported ? "UNAVAILABLE" is not
>>> commonly associated with a "fault".
>>>
>>> Guenter
>>>
>> FAN_POWER_UNAVAILABLE signals that the power value is not supported.
>> Would it be more suitable to drop the fault attributes and just return -ENODATA in such a case?
>>
> There should be no fault attributes unless a real fault
> is reported, and if power reporting is not supported the
> hwmon_power_input attribute should not even be created.
>
> The same really applies to the fan speed atribute: If reading
> the fan speed is not supported, the attribute should not even
> exist.
>
> Guenter
>
I see, however it seems that some ACPI implementations also return a fan speed of 0xffffffff
to signal an error, so we cannot use this value to check if the BIOS supports fan speed
reporting.

I will send a v4 patch witch will drop the fault attributes. When encountering a fan speed
of 0xffffffff, returning -ENODATA should be ok i think.

Thanks,
Armin Wolf


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