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Sender: Guenter Roeck <groeck7@gmail.com>
Date: Fri, 12 Apr 2024 14:01:30 -0700
From: Guenter Roeck <linux@roeck-us.net>
To: Armin Wolf <W_Armin@gmx.de>
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
Subject: Re: [PATCH v3 2/2] ACPI: fan: Add hwmon support
Message-ID: <cff6f5f3-d883-4509-819d-9d2307bdcd56@roeck-us.net>
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>
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In-Reply-To: <aace96e3-8645-469b-9056-0199af9d220c@gmx.de>

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