Documentation/hwmon/hp-wmi-sensors.rst
.. SPDX-License-Identifier: GPL-2.0-or-later
.. include:: <isonum.txt>
:Copyright: |copy| 2023 James Seo [email protected]
Hewlett-Packard (and some HP Compaq) business-class computers report hardware
monitoring information via Windows Management Instrumentation (WMI).
This driver exposes that information to the Linux hwmon subsystem, allowing
userspace utilities like sensors to gather numeric sensor readings.
When the driver is loaded, it discovers the sensors available on the
system and creates the following sysfs attributes as necessary within
/sys/class/hwmon/hwmon[X]:
([X] is some number that depends on other system components.)
======================= ======= ===================================
Name Perm Description
======================= ======= ===================================
curr[X]_input RO Current in milliamperes (mA).
curr[X]_label RO Current sensor label.
fan[X]_input RO Fan speed in RPM.
fan[X]_label RO Fan sensor label.
fan[X]_fault RO Fan sensor fault indicator.
fan[X]_alarm RO Fan sensor alarm indicator.
in[X]_input RO Voltage in millivolts (mV).
in[X]_label RO Voltage sensor label.
temp[X]_input RO Temperature in millidegrees Celsius
(m\ |deg|\ C).
temp[X]_label RO Temperature sensor label.
temp[X]_fault RO Temperature sensor fault indicator.
temp[X]_alarm RO Temperature sensor alarm indicator.
intrusion[X]_alarm RW Chassis intrusion alarm indicator.
======================= ======= ===================================
fault attributes
Reading 1 instead of 0 as the fault attribute for a sensor
indicates that it has encountered some issue during operation such that
measurements from it should not be trusted. If a sensor with the fault
condition recovers later, reading this attribute will return 0 again.
alarm attributes
Reading 1 instead of 0 as the alarm attribute for a sensor
indicates that one of the following has occurred, depending on its type:
fan: The fan has stalled or has been disconnected while running.temp: The sensor reading has reached a critical threshold.
The exact threshold is system-dependent.intrusion: The system's chassis has been opened.After 1 is read from an alarm attribute, the attribute resets itself
and returns 0 on subsequent reads. As an exception, an
intrusion[X]_alarm can only be manually reset by writing 0 to it.
.. warning:: The debugfs interface is subject to change without notice
and is only available when the kernel is compiled with
CONFIG_DEBUG_FS defined.
The standard hwmon interface in sysfs exposes sensors of several common types
that are connected as of driver initialization. However, there are usually
other sensors in WMI that do not meet these criteria. In addition, a number of
system-dependent "platform events objects" used for alarm attributes may
be present. A debugfs interface is therefore provided for read-only access to
all available HP WMI sensors and platform events objects.
/sys/kernel/debug/hp-wmi-sensors-[X]/sensor
contains one numbered entry per sensor with the following attributes:
=============================== =======================================
Name Example
=============================== =======================================
name CPU0 Fan
description Reports CPU0 fan speed
sensor_type 12
other_sensor_type (an empty string)
operational_status 2
possible_states Normal,Caution,Critical,Not Present
current_state Normal
base_units 19
unit_modifier 0
current_reading 1008
rate_units 0 (only exists on some systems)
=============================== =======================================
If platform events objects are available,
/sys/kernel/debug/hp-wmi-sensors-[X]/platform_events
contains one numbered entry per object with the following attributes:
=============================== ====================
Name Example
=============================== ====================
name CPU0 Fan Stall
description CPU0 Fan Speed
source_namespace root\wmi
source_class HPBIOS_BIOSEvent
category 3
possible_severity 25
possible_status 5
=============================== ====================
These represent the properties of the underlying HPBIOS_BIOSNumericSensor
and HPBIOS_PlatformEvents WMI objects, which vary between systems.
See [#]_ for more details and Managed Object Format (MOF) definitions.
alarm attributes will be unavailable even on systems that
support them. This is because the same WMI event GUID used by this driver
for alarm attributes is used on those systems for e.g. laptop hotkeys... [#] Hewlett-Packard Development Company, L.P., "HP Client Management Interface Technical White Paper", 2005. [Online]. Available: https://h20331.www2.hp.com/hpsub/downloads/cmi_whitepaper.pdf