Re: [PATCH v3 2/2] ACPI: fan: Add hwmon support

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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





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