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

[Armin Wolf]

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