141 lines · plain
1.. SPDX-License-Identifier: GPL-2.0-or-later2 3.. include:: <isonum.txt>4 5===========================6Linux HP WMI Sensors Driver7===========================8 9:Copyright: |copy| 2023 James Seo <james@equiv.tech>10 11Description12===========13 14Hewlett-Packard (and some HP Compaq) business-class computers report hardware15monitoring information via Windows Management Instrumentation (WMI).16This driver exposes that information to the Linux hwmon subsystem, allowing17userspace utilities like ``sensors`` to gather numeric sensor readings.18 19sysfs interface20===============21 22When the driver is loaded, it discovers the sensors available on the23system and creates the following sysfs attributes as necessary within24``/sys/class/hwmon/hwmon[X]``:25 26(``[X]`` is some number that depends on other system components.)27 28======================= ======= ===================================29Name Perm Description30======================= ======= ===================================31``curr[X]_input`` RO Current in milliamperes (mA).32``curr[X]_label`` RO Current sensor label.33``fan[X]_input`` RO Fan speed in RPM.34``fan[X]_label`` RO Fan sensor label.35``fan[X]_fault`` RO Fan sensor fault indicator.36``fan[X]_alarm`` RO Fan sensor alarm indicator.37``in[X]_input`` RO Voltage in millivolts (mV).38``in[X]_label`` RO Voltage sensor label.39``temp[X]_input`` RO Temperature in millidegrees Celsius40 (m\ |deg|\ C).41``temp[X]_label`` RO Temperature sensor label.42``temp[X]_fault`` RO Temperature sensor fault indicator.43``temp[X]_alarm`` RO Temperature sensor alarm indicator.44``intrusion[X]_alarm`` RW Chassis intrusion alarm indicator.45======================= ======= ===================================46 47``fault`` attributes48 Reading ``1`` instead of ``0`` as the ``fault`` attribute for a sensor49 indicates that it has encountered some issue during operation such that50 measurements from it should not be trusted. If a sensor with the fault51 condition recovers later, reading this attribute will return ``0`` again.52 53``alarm`` attributes54 Reading ``1`` instead of ``0`` as the ``alarm`` attribute for a sensor55 indicates that one of the following has occurred, depending on its type:56 57 - ``fan``: The fan has stalled or has been disconnected while running.58 - ``temp``: The sensor reading has reached a critical threshold.59 The exact threshold is system-dependent.60 - ``intrusion``: The system's chassis has been opened.61 62 After ``1`` is read from an ``alarm`` attribute, the attribute resets itself63 and returns ``0`` on subsequent reads. As an exception, an64 ``intrusion[X]_alarm`` can only be manually reset by writing ``0`` to it.65 66debugfs interface67=================68 69.. warning:: The debugfs interface is subject to change without notice70 and is only available when the kernel is compiled with71 ``CONFIG_DEBUG_FS`` defined.72 73The standard hwmon interface in sysfs exposes sensors of several common types74that are connected as of driver initialization. However, there are usually75other sensors in WMI that do not meet these criteria. In addition, a number of76system-dependent "platform events objects" used for ``alarm`` attributes may77be present. A debugfs interface is therefore provided for read-only access to78all available HP WMI sensors and platform events objects.79 80``/sys/kernel/debug/hp-wmi-sensors-[X]/sensor``81contains one numbered entry per sensor with the following attributes:82 83=============================== =======================================84Name Example85=============================== =======================================86``name`` ``CPU0 Fan``87``description`` ``Reports CPU0 fan speed``88``sensor_type`` ``12``89``other_sensor_type`` (an empty string)90``operational_status`` ``2``91``possible_states`` ``Normal,Caution,Critical,Not Present``92``current_state`` ``Normal``93``base_units`` ``19``94``unit_modifier`` ``0``95``current_reading`` ``1008``96``rate_units`` ``0`` (only exists on some systems)97=============================== =======================================98 99If platform events objects are available,100``/sys/kernel/debug/hp-wmi-sensors-[X]/platform_events``101contains one numbered entry per object with the following attributes:102 103=============================== ====================104Name Example105=============================== ====================106``name`` ``CPU0 Fan Stall``107``description`` ``CPU0 Fan Speed``108``source_namespace`` ``root\wmi``109``source_class`` ``HPBIOS_BIOSEvent``110``category`` ``3``111``possible_severity`` ``25``112``possible_status`` ``5``113=============================== ====================114 115These represent the properties of the underlying ``HPBIOS_BIOSNumericSensor``116and ``HPBIOS_PlatformEvents`` WMI objects, which vary between systems.117See [#]_ for more details and Managed Object Format (MOF) definitions.118 119Known issues and limitations120============================121 122- If the existing hp-wmi driver for non-business-class HP systems is already123 loaded, ``alarm`` attributes will be unavailable even on systems that124 support them. This is because the same WMI event GUID used by this driver125 for ``alarm`` attributes is used on those systems for e.g. laptop hotkeys.126- Dubious sensor hardware and inconsistent BIOS WMI implementations have been127 observed to cause inaccurate readings and peculiar behavior, such as alarms128 failing to occur or occurring only once per boot.129- Only temperature, fan speed, and intrusion sensor types have been seen in130 the wild so far. Support for voltage and current sensors is therefore131 provisional.132- Although HP WMI sensors may claim to be of any type, any oddball sensor133 types unknown to hwmon will not be supported.134 135References136==========137 138.. [#] Hewlett-Packard Development Company, L.P.,139 "HP Client Management Interface Technical White Paper", 2005. [Online].140 Available: https://h20331.www2.hp.com/hpsub/downloads/cmi_whitepaper.pdf141