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