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

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Date: Fri, 12 Apr 2024 14:01:30 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Armin Wolf <W_Armin@....de>
Cc: mlj@...elec.com, rafael.j.wysocki@...el.com, lenb@...nel.org,
	jdelvare@...e.com, linux@...ssschuh.net,
	ilpo.jarvinen@...ux.intel.com, linux-acpi@...r.kernel.org,
	linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
	platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v3 2/2] ACPI: fan: Add hwmon support

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