[RFC 07/11] Documentation/hwmon: Revise sysfs interface specification
From: James Seo
Date: Thu May 04 2023 - 04:13:28 EST
Reorganize content into coherent sections.
Shorten long attribute descriptions (save them for the ABI).
Mark the section on interpreting attribute writes as outdated.
Fix minor issues (typos, grammar, etc.) and add markup.
Signed-off-by: James Seo <james@xxxxxxxxxx>
---
Documentation/hwmon/sysfs-interface.rst | 984 +++++++++++-------------
1 file changed, 440 insertions(+), 544 deletions(-)
diff --git a/Documentation/hwmon/sysfs-interface.rst b/Documentation/hwmon/sysfs-interface.rst
index f76e9f8cc1ad..ab93554578ac 100644
--- a/Documentation/hwmon/sysfs-interface.rst
+++ b/Documentation/hwmon/sysfs-interface.rst
@@ -1,15 +1,21 @@
+================================================
Naming and data format standards for sysfs files
================================================
-The libsensors library offers an interface to the raw sensors data
-through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
-completely chip-independent. It assumes that all the kernel drivers
-implement the standard sysfs interface described in this document.
+.. contents::
+
+Introduction
+============
+
+The ``libsensors`` library offers an interface to the raw sensors data
+through the ``sysfs`` interface. Since ``lm-sensors`` 3.0.0, ``libsensors``
+is completely chip-independent. It assumes that all the kernel drivers
+implement the standard ``sysfs`` interface described in this document.
This makes adding or updating support for any given chip very easy, as
-libsensors, and applications using it, do not need to be modified.
-This is a major improvement compared to lm-sensors 2.
+``libsensors``, and applications using it, do not need to be modified.
+This is a major improvement compared to ``lm-sensors`` 2.
-Note that motherboards vary widely in the connections to sensor chips.
+Note that motherboards vary widely in their connections to sensor chips.
There is no standard that ensures, for example, that the second
temperature sensor is connected to the CPU, or that the second fan is on
the CPU. Also, some values reported by the chips need some computation
@@ -19,638 +25,528 @@ range using external resistors. Since the values of these resistors
can change from motherboard to motherboard, the conversions cannot be
hard coded into the driver and have to be done in user space.
-For this reason, even if we aim at a chip-independent libsensors, it will
-still require a configuration file (e.g. /etc/sensors.conf) for proper
+For this reason, even if we aim at a chip-independent ``libsensors``, it will
+still require a configuration file (e.g.``/etc/sensors3.conf``) for proper
values conversion, labeling of inputs and hiding of unused inputs.
-An alternative method that some programs use is to access the sysfs
+An alternative method that some programs use is to access the ``sysfs``
files directly. This document briefly describes the standards that the
drivers follow, so that an application program can scan for entries and
access this data in a simple and consistent way. That said, such programs
will have to implement conversion, labeling and hiding of inputs. For
this reason, it is still not recommended to bypass the library.
-Each chip gets its own directory in the sysfs /sys/devices tree. To
+Each chip gets its own directory in the ``sysfs`` ``/sys/devices`` tree. To
find all sensor chips, it is easier to follow the device symlinks from
-`/sys/class/hwmon/hwmon*`.
-
-Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
-in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
-in the hwmon "class" device directory are also supported. Complex drivers
-(e.g. drivers for multifunction chips) may want to use this possibility to
-avoid namespace pollution. The only drawback will be that older versions of
-libsensors won't support the driver in question.
-
-All sysfs values are fixed point numbers.
-
-There is only one value per file, unlike the older /proc specification.
-The common scheme for files naming is: <type><number>_<item>. Usual
-types for sensor chips are "in" (voltage), "temp" (temperature) and
-"fan" (fan). Usual items are "input" (measured value), "max" (high
-threshold, "min" (low threshold). Numbering usually starts from 1,
-except for voltages which start from 0 (because most data sheets use
-this). A number is always used for elements that can be present more
-than once, even if there is a single element of the given type on the
-specific chip. Other files do not refer to a specific element, so
-they have a simple name, and no number.
-
-Alarms are direct indications read from the chips. The drivers do NOT
-make comparisons of readings to thresholds. This allows violations
-between readings to be caught and alarmed. The exact definition of an
-alarm (for example, whether a threshold must be met or must be exceeded
-to cause an alarm) is chip-dependent.
+``/sys/class/hwmon/hwmon*``.
-When setting values of hwmon sysfs attributes, the string representation of
-the desired value must be written, note that strings which are not a number
-are interpreted as 0! For more on how written strings are interpreted see the
-"sysfs attribute writes interpretation" section at the end of this file.
+Up to ``lm-sensors`` 3.0.0, ``libsensors`` looks for hardware monitoring
+attributes in the ``physical`` device directory. Since ``lm-sensors`` 3.0.1,
+attributes found in the ``hwmon`` ``class`` device directory are also
+supported. Complex drivers (e.g. drivers for multifunction chips) may want to
+use this possibility to avoid namespace pollution. The only drawback will be
+that older versions of ``libsensors`` won't support the driver in question.
-Attribute access
-----------------
+Interface specification
+=======================
-Hardware monitoring sysfs attributes are displayed by unrestricted userspace
-applications. For this reason, all standard ABI attributes shall be world
-readable. Writeable standard ABI attributes shall be writeable only for
-privileged users.
+All ``sysfs`` values are fixed point numbers. There is only one value per
+file, unlike the older ``/proc`` specification.
--------------------------------------------------------------------------
+Names
+-----
-======= ===========================================
-`[0-*]` denotes any positive number starting from 0
-`[1-*]` denotes any positive number starting from 1
-RO read only value
-WO write only value
-RW read/write value
-======= ===========================================
+The common scheme for file naming is: ``<type><number>_<item>``.
-Read/write values may be read-only for some chips, depending on the
-hardware implementation.
-
-All entries (except name) are optional, and should only be created in a
-given driver if the chip has the feature.
+Usual types for sensor chips are ``in`` (voltage), ``temp`` (temperature), and
+``fan`` (fan).
-See Documentation/ABI/testing/sysfs-class-hwmon for a complete description
-of the attributes.
+Usual items are ``input`` (measured value), ``max`` (high threshold), and
+``min`` (low threshold).
-*****************
-Global attributes
-*****************
+Numbering usually starts from ``1``, except for voltages, which start from
+``0`` (because most data sheets use this). A number is always used for
+elements that can be present more than once, even if there is a single
+element of the given type on the specific chip. Other files do not refer
+to a specific element, so they have a simple name, and no number.
-`name`
- The chip name.
+Access modes
+------------
-`label`
- A descriptive label that allows to uniquely identify a device
- within the system.
-
-`update_interval`
- The interval at which the chip will update readings.
+Hardware monitoring ``sysfs`` attributes are displayed by unrestricted
+userspace applications. For this reason, all standard ABI attributes shall be
+world readable. Writeable standard ABI attributes shall be writeable only for
+privileged users.
+Setting attributes
+------------------
-********
-Voltages
-********
+When setting values of ``hwmon`` ``sysfs`` attributes, the string
+representation of the desired value must be written.
-`in[0-*]_min`
- Voltage min value.
+Interpreting writes to attributes
+---------------------------------
-`in[0-*]_lcrit`
- Voltage critical min value.
+.. warning ::
+ This section is outdated and in need of attention. Please use
+ this information with caution, and please consider sending patches
+ to update it.
-`in[0-*]_max`
- Voltage max value.
+Note that strings which are not a number are interpreted as ``0``!
-`in[0-*]_crit`
- Voltage critical max value.
+``hwmon`` ``sysfs`` attributes always contain numbers, so the first thing to
+do is to convert the input to a number. There are 2 ways to do this depending
+on whether the number can be negative or not:
-`in[0-*]_input`
- Voltage input value.
+.. code-block:: c
-`in[0-*]_average`
- Average voltage
+ unsigned long u = simple_strtoul(buf, NULL, 10);
+ long s = simple_strtol(buf, NULL, 10);
-`in[0-*]_lowest`
- Historical minimum voltage
+with **buf** being the buffer with the user input being passed by the kernel.
+Notice that we do not use the second argument of strto[u]l, and thus cannot
+tell when ``0`` is returned, if this was really ``0`` or is caused by invalid
+input. This is done deliberately as checking this everywhere would add a lot
+of code to the kernel.
-`in[0-*]_highest`
- Historical maximum voltage
+Notice that it is important to always store the converted value in an
+unsigned long or long, so that no wrap around can happen before any further
+checking.
-`in[0-*]_reset_history`
- Reset inX_lowest and inX_highest
+After the input string is converted to an (unsigned) long, the value should be
+checked if its acceptable. Be careful with further conversions on the value
+before checking it for validity, as these conversions could still cause a wrap
+around before the check. For example do not multiply the result, and only
+add/subtract if it has been divided before the add/subtract.
-`in_reset_history`
- Reset inX_lowest and inX_highest for all sensors
+What to do if a value is found to be invalid depends on the type of the
+sysfs attribute that is being set. If it is a continuous setting like a
+``tempX_max`` or ``inX_max`` attribute, then the value should be clamped to
+its limits using clamp_val(value, min_limit, max_limit). If it is not
+continuous, like for example a ``tempX_type``, then when an invalid value is
+written, ``-EINVAL`` should be returned.
-`in[0-*]_label`
- Suggested voltage channel label.
+Example1, ``temp1_max``, register is a signed 8-bit value (-128 - 127 degrees):
-`in[0-*]_enable`
- Enable or disable the sensors.
+.. code-block:: c
-`cpu[0-*]_vid`
- CPU core reference voltage.
+ long v = simple_strtol(buf, NULL, 10) / 1000;
+ v = clamp_val(v, -128, 127);
+ /* write v to register */
-`vrm`
- Voltage Regulator Module version number.
+Example2, fan divider setting, valid values ``2``, ``4`` and ``8``:
-`in[0-*]_rated_min`
- Minimum rated voltage.
+.. code-block:: c
-`in[0-*]_rated_max`
- Maximum rated voltage.
+ unsigned long v = simple_strtoul(buf, NULL, 10);
-Also see the Alarms section for status flags associated with voltages.
+ switch (v) {
+ case 2: v = 1; break;
+ case 4: v = 2; break;
+ case 8: v = 3; break;
+ default:
+ return -EINVAL;
+ }
+ /* write v to register */
-****
-Fans
-****
+Standard attributes
+===================
-`fan[1-*]_min`
- Fan minimum value
+See ``Documentation/ABI/testing/sysfs-class-hwmon`` for a complete description
+of standard attributes, including units, allowed values, error codes, and
+required behaviors.
-`fan[1-*]_max`
- Fan maximum value
+========= ================================================
+Text Meaning
+========= ================================================
+``[0-*]`` Denotes any positive number starting from ``0``.
+``[1-*]`` Denotes any positive number starting from ``1``.
+**RO** Read-only value.
+**WO** Write-only value.
+**RW** Read/write value.
-`fan[1-*]_input`
- Fan input value.
+ May be read-only for some chips, depending on
+ the hardware implementation.
+========= ================================================
-`fan[1-*]_div`
- Fan divisor.
+All entries (except ``name``) are optional, and should only be created in a
+given driver if the chip has the feature.
-`fan[1-*]_pulses`
- Number of tachometer pulses per fan revolution.
+Attributes by type
+------------------
-`fan[1-*]_target`
- Desired fan speed
+Global
+~~~~~~
-`fan[1-*]_label`
- Suggested fan channel label.
+=================== ====== =============================
+Name Perms Description
+=================== ====== =============================
+``name`` **RO** Chip name.
+``label`` **RO** Chip label.
+``update_interval`` **RW** Chip reading update interval.
+=================== ====== =============================
-`fan[1-*]_enable`
- Enable or disable the sensors.
+Also see `Alarms`_ and `Averages`_ for additional attributes.
-Also see the Alarms section for status flags associated with fans.
+Voltages
+~~~~~~~~
+
+========================= ====== =========================================
+Name Perms Description
+========================= ====== =========================================
+``in[0-*]_min`` **RW** Voltage min value.
+``in[0-*]_lcrit`` **RW** Voltage critical min value.
+``in[0-*]_max`` **RW** Voltage max value.
+``in[0-*]_crit`` **RW** Voltage critical max value.
+``in[0-*]_input`` **RO** Voltage input value.
+``in[0-*]_average`` **RO** Average voltage.
+``in[0-*]_lowest`` **RO** Historical minimum voltage.
+``in[0-*]_highest`` **RO** Historical maximum voltage.
+``in[0-*]_reset_history`` **WO** Reset ``in[0-*]_lowest`` and
+ ``in[0-*]_highest``.
+``in_reset_history`` **WO** Reset ``lowest`` and ``highest``
+ for all ``in[0-*]`` sensors.
+``in[0-*]_label`` **RO** Suggested voltage channel label.
+``in[0-*]_enable`` **RW** Enable or disable the sensor.
+``cpu[0-*]_vid`` **RO** CPU core reference voltage.
+``vrm`` **RW** Voltage Regulator Module version number.
+``in[0-*]_rated_min`` **RO** Minimum rated voltage.
+``in[0-*]_rated_max`` **RO** Maximum rated voltage.
+========================= ====== =========================================
+
+Also see `Alarms`_ and `Averages`_ for status flags and additional attributes
+associated with voltages.
+Fans
+~~~~
+
+=================== ====== ===============================================
+Name Perms Description
+=================== ====== ===============================================
+``fan[1-*]_min`` **RW** Fan minimum value.
+``fan[1-*]_max`` **RW** Fan maximum value.
+``fan[1-*]_input`` **RO** Fan input value.
+``fan[1-*]_div`` **RW** Fan divisor.
+``fan[1-*]_pulses`` **RW** Number of tachometer pulses per fan revolution.
+``fan[1-*]_target`` **RW** Desired fan speed.
+``fan[1-*]_label`` **RO** Suggested fan channel label.
+``fan[1-*]_enable`` **RW** Enable or disable the sensor.
+=================== ====== ===============================================
+
+Also see `Alarms and faults`_ for status flags and additional attributes
+associated with fans.
-***
PWM
-***
-
-`pwm[1-*]`
- Pulse width modulation fan control.
-
-`pwm[1-*]_enable`
- Fan speed control method.
-
-`pwm[1-*]_mode`
- direct current or pulse-width modulation.
-
-`pwm[1-*]_freq`
- Base PWM frequency in Hz.
-
-`pwm[1-*]_auto_channels_temp`
- Select which temperature channels affect this PWM output in
- auto mode.
-
-`pwm[1-*]_auto_point[1-*]_pwm` / `pwm[1-*]_auto_point[1-*]_temp` / `pwm[1-*]_auto_point[1-*]_temp_hyst`
- Define the PWM vs temperature curve.
-
-`temp[1-*]_auto_point[1-*]_pwm` / `temp[1-*]_auto_point[1-*]_temp` / `temp[1-*]_auto_point[1-*]_temp_hyst`
- Define the PWM vs temperature curve.
-
-There is a third case where trip points are associated to both PWM output
-channels and temperature channels: the PWM values are associated to PWM
-output channels while the temperature values are associated to temperature
+~~~
+
++-------------------------------------------+--------+-------------------------------------+
+| Name | Perms | Description |
++===========================================+========+=====================================+
+| ``pwm[1-*]`` | **RW** | Pulse-width modulation fan control. |
++-------------------------------------------+--------+-------------------------------------+
+| ``pwm[1-*]_enable`` | **RW** | Fan speed control method. |
++-------------------------------------------+--------+-------------------------------------+
+| ``pwm[1-*]_mode`` | **RW** | Fan speed control mode. |
++-------------------------------------------+--------+-------------------------------------+
+| ``pwm[1-*]_freq`` | **RW** | Base PWM frequency in Hz. |
++-------------------------------------------+--------+-------------------------------------+
+| ``pwm[1-*]_auto_channels_temp`` | **RW** | Auto mode channel mask. |
++-------------------------------------------+--------+-------------------------------------+
+| | ``pwm[1-*]_auto_point[1-*]_pwm`` | **RW** | PWM temperature curve definition |
+| | ``pwm[1-*]_auto_point[1-*]_temp`` | | for chips that associate trip |
+| | ``pwm[1-*]_auto_point[1-*]_temp_hyst`` | | points with PWM output channels. |
++-------------------------------------------+--------+-------------------------------------+
+| | ``temp[1-*]_auto_point[1-*]_pwm`` | **RW** | PWM temperature curve definition |
+| | ``temp[1-*]_auto_point[1-*]_temp`` | | for chips that associate trip |
+| | ``temp[1-*]_auto_point[1-*]_temp_hyst`` | | points with temperature channels. |
++-------------------------------------------+--------+-------------------------------------+
+
+Please see ``Documentation/ABI/testing/sysfs-class-hwmon`` for more
+information on PWM vs. temperature curves.
+
+There is a third case where trip points are associated with both PWM output
+channels and temperature channels: the PWM values are associated with PWM
+output channels while the temperature values are associated with temperature
channels. In that case, the result is determined by the mapping between
temperature inputs and PWM outputs. When several temperature inputs are
mapped to a given PWM output, this leads to several candidate PWM values.
The actual result is up to the chip, but in general the highest candidate
value (fastest fan speed) wins.
-
-************
Temperatures
-************
-
-`temp[1-*]_type`
- Sensor type selection.
-
-`temp[1-*]_max`
- Temperature max value.
-
-`temp[1-*]_min`
- Temperature min value.
-
-`temp[1-*]_max_hyst`
- Temperature hysteresis value for max limit.
-
-`temp[1-*]_min_hyst`
- Temperature hysteresis value for min limit.
-
-`temp[1-*]_input`
- Temperature input value.
-
-`temp[1-*]_crit`
- Temperature critical max value, typically greater than
- corresponding temp_max values.
-
-`temp[1-*]_crit_hyst`
- Temperature hysteresis value for critical limit.
-
-`temp[1-*]_emergency`
- Temperature emergency max value, for chips supporting more than
- two upper temperature limits.
-
-`temp[1-*]_emergency_hyst`
- Temperature hysteresis value for emergency limit.
-
-`temp[1-*]_lcrit`
- Temperature critical min value, typically lower than
- corresponding temp_min values.
-
-`temp[1-*]_lcrit_hyst`
- Temperature hysteresis value for critical min limit.
-
-`temp[1-*]_offset`
- Temperature offset which is added to the temperature reading
- by the chip.
-
-`temp[1-*]_label`
- Suggested temperature channel label.
-
-`temp[1-*]_lowest`
- Historical minimum temperature
-
-`temp[1-*]_highest`
- Historical maximum temperature
-
-`temp[1-*]_reset_history`
- Reset temp_lowest and temp_highest
-
-`temp_reset_history`
- Reset temp_lowest and temp_highest for all sensors
-
-`temp[1-*]_enable`
- Enable or disable the sensors.
-
-`temp[1-*]_rated_min`
- Minimum rated temperature.
-
-`temp[1-*]_rated_max`
- Maximum rated temperature.
+~~~~~~~~~~~~
+
+============================ ====== ===========================================
+Name Perms Description
+============================ ====== ===========================================
+``temp[1-*]_type`` **RW** Sensor type selection.
+``temp[1-*]_max`` **RW** Temperature max value.
+``temp[1-*]_min`` **RW** Temperature min value.
+``temp[1-*]_max_hyst`` **RW** Temperature hysteresis value for max limit.
+``temp[1-*]_min_hyst`` **RW** Temperature hysteresis value for min limit.
+``temp[1-*]_input`` **RO** Temperature input value.
+``temp[1-*]_crit`` **RW** Temperature critical max value.
+``temp[1-*]_crit_hyst`` **RW** Temperature hysteresis value
+ for critical limit.
+``temp[1-*]_emergency`` **RW** Temperature emergency max value.
+``temp[1-*]_emergency_hyst`` **RW** Temperature hysteresis value
+ for emergency limit.
+``temp[1-*]_lcrit`` **RW** Temperature critical min value.
+``temp[1-*]_lcrit_hyst`` **RW** Temperature hysteresis value
+ for critical min limit.
+``temp[1-*]_offset`` **RW** Temperature offset.
+``temp[1-*]_label`` **RO** Suggested temperature channel label.
+``temp[1-*]_lowest`` **RO** Historical minimum temperature.
+``temp[1-*]_highest`` **RO** Historical maximum temperature.
+``temp[1-*]_reset_history`` **WO** Reset ``temp[1-*]_lowest`` and
+ ``temp[1-*]_highest``.
+``temp_reset_history`` **WO** Reset ``lowest`` and ``highest``
+ for all ``temp[1-*]`` sensors.
+``temp[1-*]_enable`` **RW** Enable or disable the sensor.
+``temp[1-*]_rated_min`` **RO** Minimum rated temperature.
+``temp[1-*]_rated_max`` **RO** Maximum rated temperature.
+============================ ====== ===========================================
Some chips measure temperature using external thermistors and an ADC, and
report the temperature measurement as a voltage. Converting this voltage
back to a temperature (or the other way around for limits) requires
mathematical functions not available in the kernel, so the conversion
-must occur in user space. For these chips, all temp* files described
+must occur in user space. For these chips, all ``temp*`` files described
above should contain values expressed in millivolt instead of millidegree
Celsius. In other words, such temperature channels are handled as voltage
channels by the driver.
-Also see the Alarms section for status flags associated with temperatures.
+Also see `Alarms and faults`_ and `Averages`_ for status flags and additional
+attributes associated with temperatures.
-
-********
Currents
-********
-
-`curr[1-*]_max`
- Current max value.
-
-`curr[1-*]_min`
- Current min value.
-
-`curr[1-*]_lcrit`
- Current critical low value
-
-`curr[1-*]_crit`
- Current critical high value.
-
-`curr[1-*]_input`
- Current input value.
-
-`curr[1-*]_average`
- Average current use.
-
-`curr[1-*]_lowest`
- Historical minimum current.
-
-`curr[1-*]_highest`
- Historical maximum current.
+~~~~~~~~
+
+=========================== ====== ================================
+Name Perms Description
+=========================== ====== ================================
+``curr[1-*]_max`` **RW** Current max value.
+``curr[1-*]_min`` **RW** Current min value.
+``curr[1-*]_lcrit`` **RW** Current critical min value.
+``curr[1-*]_crit`` **RW** Current critical max value.
+``curr[1-*]_input`` **RO** Current input value.
+``curr[1-*]_average`` **RO** Average current use.
+``curr[1-*]_lowest`` **RO** Historical minimum current.
+``curr[1-*]_highest`` **RO** Historical maximum current.
+``curr[1-*]_reset_history`` **WO** Reset ``curr[1-*]_lowest`` and
+ ``curr[1-*]_highest``.
+``curr_reset_history`` **WO** Reset ``lowest`` and ``highest``
+ for all ``curr[1-*]`` sensors.
+``curr[1-*]_enable`` **RW** Enable or disable the sensor.
+``curr[1-*]_rated_min`` **RO** Minimum rated current.
+``curr[1-*]_rated_max`` **RO** Maximum rated current.
+=========================== ====== ================================
+
+Also see `Alarms`_ and `Averages`_ for status flags and additional attributes
+associated with currents.
-`curr[1-*]_reset_history`
- Reset currX_lowest and currX_highest
-
- WO
-
-`curr_reset_history`
- Reset currX_lowest and currX_highest for all sensors.
-
-`curr[1-*]_enable`
- Enable or disable the sensors.
-
-`curr[1-*]_rated_min`
- Minimum rated current.
-
-`curr[1-*]_rated_max`
- Maximum rated current.
-
-Also see the Alarms section for status flags associated with currents.
-
-*****
Power
-*****
-
-`power[1-*]_average`
- Average power use.
-
-`power[1-*]_average_interval`
- Power use averaging interval.
+~~~~~
+
++-------------------------------------+--------+---------------------------------------+
+| Name | Perms | Description |
++=====================================+========+=======================================+
+| ``power[1-*]_average`` | **RO** | Average power use. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_interval`` | **RW** | Power use averaging interval. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_interval_max`` | **RO** | Maximum power use averaging interval. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_interval_min`` | **RO** | Minimum power use averaging interval. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_highest`` | **RO** | Historical average maximum power use. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_lowest`` | **RO** | Historical average minimum power use. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_max`` | **RW** | Maximum average power |
+| | | notification threshold. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_average_min`` | **RW** | Minimum average power |
+| | | notification threshold. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_input`` | **RO** | Instantaneous power use. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_input_highest`` | **RO** | Historical maximum power use. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_input_lowest`` | **RO** | Historical minimum power use. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_reset_history`` | **WO** | | Reset ``power[1-*]_input_highest``, |
+| | | | ``power[1-*]_input_lowest``, |
+| | | | ``power[1-*]_average_highest``, and |
+| | | | ``power[1-*]_average_lowest``. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_accuracy`` | **RO** | Accuracy of the power meter. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_cap`` | **RW** | Power reduction threshold. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_cap_hyst`` | **RW** | Threshold hysteresis margin. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_cap_max`` | **RO** | Maximum cap that can be set. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_cap_min`` | **RO** | Minimum cap that can be set. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_max`` | **RW** | Maximum power. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_crit`` | **RW** | Critical power reduction threshold. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_enable`` | **RW** | Enable or disable the sensor. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_rated_min`` | **RO** | Minimum rated power. |
++-------------------------------------+--------+---------------------------------------+
+| ``power[1-*]_rated_max`` | **RO** | Maximum rated power. |
++-------------------------------------+--------+---------------------------------------+
+
+Please see ``Documentation/ABI/testing/sysfs-class-hwmon`` for more
+information on thresholds and notifications/actions.
+
+Also see `Alarms`_ and `Averages`_ for status flags and additional attributes
+associated with power readings.
-`power[1-*]_average_interval_max`
- Maximum power use averaging interval.
-
-`power[1-*]_average_interval_min`
- Minimum power use averaging interval.
-
-`power[1-*]_average_highest`
- Historical average maximum power use
-
-`power[1-*]_average_lowest`
- Historical average minimum power use
-
-`power[1-*]_average_max`
- A poll notification is sent to `power[1-*]_average` when
- power use rises above this value.
-
-`power[1-*]_average_min`
- A poll notification is sent to `power[1-*]_average` when
- power use sinks below this value.
-
-`power[1-*]_input`
- Instantaneous power use.
-
-`power[1-*]_input_highest`
- Historical maximum power use
-
-`power[1-*]_input_lowest`
- Historical minimum power use.
-
-`power[1-*]_reset_history`
- Reset input_highest, input_lowest, average_highest and
- average_lowest.
-
-`power[1-*]_accuracy`
- Accuracy of the power meter.
-
-`power[1-*]_cap`
- If power use rises above this limit, the
- system should take action to reduce power use.
-
-`power[1-*]_cap_hyst`
- Margin of hysteresis built around capping and notification.
-
-`power[1-*]_cap_max`
- Maximum cap that can be set.
-
-`power[1-*]_cap_min`
- Minimum cap that can be set.
-
-`power[1-*]_max`
- Maximum power.
-
-`power[1-*]_crit`
- Critical maximum power.
-
- If power rises to or above this limit, the
- system is expected take drastic action to reduce
- power consumption, such as a system shutdown or
- a forced powerdown of some devices.
-
- Unit: microWatt
-
- RW
-
-`power[1-*]_enable`
- Enable or disable the sensors.
-
- When disabled the sensor read will return
- -ENODATA.
-
- - 1: Enable
- - 0: Disable
-
- RW
-
-`power[1-*]_rated_min`
- Minimum rated power.
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_rated_max`
- Maximum rated power.
-
- Unit: microWatt
-
- RO
-
-Also see the Alarms section for status flags associated with power readings.
-
-******
Energy
-******
-
-`energy[1-*]_input`
- Cumulative energy use
-
- Unit: microJoule
-
- RO
-
-`energy[1-*]_enable`
- Enable or disable the sensors.
-
- When disabled the sensor read will return
- -ENODATA.
-
- - 1: Enable
- - 0: Disable
+~~~~~~
- RW
+====================== ====== =============================
+Name Perms Description
+====================== ====== =============================
+``energy[1-*]_input`` **RO** Cumulative energy use.
+``energy[1-*]_enable`` **RW** Enable or disable the sensor.
+====================== ====== =============================
-********
Humidity
-********
+~~~~~~~~
-`humidity[1-*]_input`
- Humidity.
+=========================== ====== =============================
+Name Perms Description
+=========================== ====== =============================
+``humidity[1-*]_input`` **RO** Humidity.
+``humidity[1-*]_enable`` **RW** Enable or disable the sensor.
+``humidity[1-*]_rated_min`` **RO** Minimum rated humidity.
+``humidity[1-*]_rated_max`` **RW** Maximum rated humidity.
+=========================== ====== =============================
-`humidity[1-*]_enable`
- Enable or disable the sensors.
+Intrusion
+~~~~~~~~~
-`humidity[1-*]_rated_min`
- Minimum rated humidity.
+See `Alarms`_ for more information.
-`humidity[1-*]_rated_max`
- Maximum rated humidity.
+Alarms and faults
+-----------------
-******
Alarms
-******
+~~~~~~
-Each channel or limit may have an associated alarm file, containing a
-boolean value. 1 means than an alarm condition exists, 0 means no alarm.
+Each channel or limit may have an associated ``alarm`` attribute, containing
+a boolean value. ``1`` means that an alarm condition exists, ``0`` means no
+alarm.
-Usually a given chip will either use channel-related alarms, or
-limit-related alarms, not both. The driver should just reflect the hardware
-implementation.
-
-+-------------------------------+-----------------------+
-| **`in[0-*]_alarm`, | Channel alarm |
-| `curr[1-*]_alarm`, | |
-| `power[1-*]_alarm`, | - 0: no alarm |
-| `fan[1-*]_alarm`, | - 1: alarm |
-| `temp[1-*]_alarm`** | |
-| | RO |
-+-------------------------------+-----------------------+
-
-**OR**
-
-+-------------------------------+-----------------------+
-| **`in[0-*]_min_alarm`, | Limit alarm |
-| `in[0-*]_max_alarm`, | |
-| `in[0-*]_lcrit_alarm`, | - 0: no alarm |
-| `in[0-*]_crit_alarm`, | - 1: alarm |
-| `curr[1-*]_min_alarm`, | |
-| `curr[1-*]_max_alarm`, | RO |
-| `curr[1-*]_lcrit_alarm`, | |
-| `curr[1-*]_crit_alarm`, | |
-| `power[1-*]_cap_alarm`, | |
-| `power[1-*]_max_alarm`, | |
-| `power[1-*]_crit_alarm`, | |
-| `fan[1-*]_min_alarm`, | |
-| `fan[1-*]_max_alarm`, | |
-| `temp[1-*]_min_alarm`, | |
-| `temp[1-*]_max_alarm`, | |
-| `temp[1-*]_lcrit_alarm`, | |
-| `temp[1-*]_crit_alarm`, | |
-| `temp[1-*]_emergency_alarm`** | |
-+-------------------------------+-----------------------+
-
-Each input channel may have an associated fault file. This can be used
-to notify open diodes, unconnected fans etc. where the hardware
-supports it. When this boolean has value 1, the measurement for that
-channel should not be trusted.
+Alarms are direct indications read from the chips. The drivers **do not**
+make comparisons of readings to thresholds. This allows violations
+between readings to be caught and alarmed. The exact definition of an
+alarm (for example, whether a threshold must be met or must be exceeded
+to cause an alarm) is chip-dependent.
-`fan[1-*]_fault` / `temp[1-*]_fault`
- Input fault condition.
++---------------------------------+--------+------------------------------+
+| Name | Perms | Description |
++=================================+========+==============================+
+| | ``in[0-*]_alarm`` | **RO** | Channel alarm indicator. |
+| | ``curr[1-*]_alarm`` | | |
+| | ``power[1-*]_alarm`` | | |
+| | ``fan[1-*]_alarm`` | | |
+| | ``temp[1-*]_alarm`` | | |
++---------------------------------+ +------------------------------+
+| | ``in[0-*]_min_alarm`` | | Limit alarm indicator. |
+| | ``in[0-*]_max_alarm`` | | |
+| | ``in[0-*]_lcrit_alarm`` | | |
+| | ``in[0-*]_crit_alarm`` | | |
+| | ``curr[1-*]_min_alarm`` | | |
+| | ``curr[1-*]_max_alarm`` | | |
+| | ``curr[1-*]_lcrit_alarm`` | | |
+| | ``curr[1-*]_crit_alarm`` | | |
+| | ``power[1-*]_cap_alarm`` | | |
+| | ``power[1-*]_max_alarm`` | | |
+| | ``power[1-*]_crit_alarm`` | | |
+| | ``fan[1-*]_min_alarm`` | | |
+| | ``fan[1-*]_max_alarm`` | | |
+| | ``temp[1-*]_min_alarm`` | | |
+| | ``temp[1-*]_max_alarm`` | | |
+| | ``temp[1-*]_lcrit_alarm`` | | |
+| | ``temp[1-*]_emergency_alarm`` | | |
++---------------------------------+--------+ |
+| ``temp[1-*]_crit_alarm`` | **RW** | |
++---------------------------------+ +------------------------------+
+| ``intrusion[1-*]_alarm`` | | Chassis intrusion indicator. |
++---------------------------------+--------+------------------------------+
+
+Usually a given chip will either use channel-related alarms or limit-related
+alarms, but not both. The driver should just reflect the hardware
+implementation.
Some chips also offer the possibility to get beeped when an alarm occurs:
-`beep_enable`
- Master beep enable.
-
-`in[0-*]_beep`, `curr[1-*]_beep`, `fan[1-*]_beep`, `temp[1-*]_beep`,
- Channel beep.
++-------------------------+--------+--------------------------+
+| Name | Perms | Description |
++=========================+========+==========================+
+| ``beep_enable`` | **RW** | Enable or disable beeps. |
++-------------------------+ +--------------------------+
+| | ``in[0-*]_beep`` | | Channel beep. |
+| | ``curr[1-*]_beep`` | | |
+| | ``fan[1-*]_beep`` | | |
+| | ``temp[1-*]_beep`` | | |
++-------------------------+ +--------------------------+
+| ``intrusion[1-*]_beep`` | | Chassis intrusion beep. |
++-------------------------+--------+--------------------------+
In theory, a chip could provide per-limit beep masking, but no such chip
-was seen so far.
+has been seen so far.
Old drivers provided a different, non-standard interface to alarms and
-beeps. These interface files are deprecated, but will be kept around
+beeps. These interface attributes are deprecated, but will be kept around
for compatibility reasons:
-`alarms`
- Alarm bitmask.
-
-`beep_mask`
- Bitmask for beep.
-
-
-*******************
-Intrusion detection
-*******************
-
-`intrusion[0-*]_alarm`
- Chassis intrusion detection.
-
-`intrusion[0-*]_beep`
- Chassis intrusion beep.
-
-****************************
-Average sample configuration
-****************************
-
-Devices allowing for reading {in,power,curr,temp}_average values may export
-attributes for controlling number of samples used to compute average.
-
-+--------------+---------------------------------------------------------------+
-| samples | Sets number of average samples for all types of measurements. |
-| | |
-| | RW |
-+--------------+---------------------------------------------------------------+
-| in_samples | Sets number of average samples for specific type of |
-| power_samples| measurements. |
-| curr_samples | |
-| temp_samples | Note that on some devices it won't be possible to set all of |
-| | them to different values so changing one might also change |
-| | some others. |
-| | |
-| | RW |
-+--------------+---------------------------------------------------------------+
-
-sysfs attribute writes interpretation
--------------------------------------
-
-hwmon sysfs attributes always contain numbers, so the first thing to do is to
-convert the input to a number, there are 2 ways todo this depending whether
-the number can be negative or not::
+============= ====== =================
+Name Perms Description
+============= ====== =================
+``alarms`` **RW** Alarm bitmask.
+``beep_mask`` **RW** Bitmask for beep.
+============= ====== =================
- unsigned long u = simple_strtoul(buf, NULL, 10);
- long s = simple_strtol(buf, NULL, 10);
+Faults
+~~~~~~
-With buf being the buffer with the user input being passed by the kernel.
-Notice that we do not use the second argument of strto[u]l, and thus cannot
-tell when 0 is returned, if this was really 0 or is caused by invalid input.
-This is done deliberately as checking this everywhere would add a lot of
-code to the kernel.
-
-Notice that it is important to always store the converted value in an
-unsigned long or long, so that no wrap around can happen before any further
-checking.
-
-After the input string is converted to an (unsigned) long, the value should be
-checked if its acceptable. Be careful with further conversions on the value
-before checking it for validity, as these conversions could still cause a wrap
-around before the check. For example do not multiply the result, and only
-add/subtract if it has been divided before the add/subtract.
-
-What to do if a value is found to be invalid, depends on the type of the
-sysfs attribute that is being set. If it is a continuous setting like a
-tempX_max or inX_max attribute, then the value should be clamped to its
-limits using clamp_val(value, min_limit, max_limit). If it is not continuous
-like for example a tempX_type, then when an invalid value is written,
--EINVAL should be returned.
-
-Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees)::
-
- long v = simple_strtol(buf, NULL, 10) / 1000;
- v = clamp_val(v, -128, 127);
- /* write v to register */
-
-Example2, fan divider setting, valid values 2, 4 and 8::
-
- unsigned long v = simple_strtoul(buf, NULL, 10);
+Each input channel may have an associated ``fault`` attribute. This can be
+used to notify open diodes, unconnected fans etc. where the hardware
+supports it. When this boolean has value ``1``, the measurement for that
+channel should not be trusted.
- switch (v) {
- case 2: v = 1; break;
- case 4: v = 2; break;
- case 8: v = 3; break;
- default:
- return -EINVAL;
- }
- /* write v to register */
++-----------------------+--------+--------------------------+
+| Name | Perms | Description |
++=======================+========+==========================+
+| | ``fan[1-*]_fault`` | **RO** | Channel fault indicator. |
+| | ``temp[1-*]_fault`` | | |
++-----------------------+--------+--------------------------+
+
+Averages
+--------
+
+Devices allowing for reading ``average`` values may export attributes for
+controlling the number of samples used to compute the average.
+
++---------------------+--------+-------------------------------------------+
+| Name | Perms | Description |
++=====================+========+===========================================+
+| ``samples`` | **RW** | Samples in calculated average. |
++---------------------+ +-------------------------------------------+
+| | ``in_samples`` | | Samples in calculated average |
+| | ``power_samples`` | | for a specific sensor type. |
+| | ``curr_samples`` | | |
+| | ``temp_samples`` | | Note that on some devices, it won't be |
+| | | possible to set all of these to different |
+| | | values, as changing one might also change |
+| | | others. |
++---------------------+--------+-------------------------------------------+
--
2.34.1