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Date: Sat, 13 Apr 2024 01:18:51 +0200
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Subject: Re: [PATCH v3 2/2] ACPI: fan: Add hwmon support
To: Guenter Roeck <linux@roeck-us.net>
Cc: mlj@danelec.com, rafael.j.wysocki@intel.com, lenb@kernel.org,
 jdelvare@suse.com, linux@weissschuh.net, ilpo.jarvinen@linux.intel.com,
 linux-acpi@vger.kernel.org, linux-hwmon@vger.kernel.org,
 linux-kernel@vger.kernel.org, platform-driver-x86@vger.kernel.org
References: <20240412160857.79858-1-W_Armin@gmx.de>
 <20240412160857.79858-2-W_Armin@gmx.de>
 <4a07f4d1-bbee-445c-a7cc-377506de850d@roeck-us.net>
 <aace96e3-8645-469b-9056-0199af9d220c@gmx.de>
 <cff6f5f3-d883-4509-819d-9d2307bdcd56@roeck-us.net>
Content-Language: en-US
From: Armin Wolf <W_Armin@gmx.de>
In-Reply-To: <cff6f5f3-d883-4509-819d-9d2307bdcd56@roeck-us.net>
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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