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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date: Sat, 13 Apr 2024 01:18:51 +0200
From: Armin Wolf <W_Armin@....de>
To: Guenter Roeck <linux@...ck-us.net>
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

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