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authorMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-04-17 06:46:29 -0300
committerGuenter Roeck <linux@roeck-us.net>2019-04-17 10:37:23 -0700
commit7ebd8b66dd9e5a0b65e5ee5e2b8e7ca382ec97b7 (patch)
tree9db30159bd32bec125c7d49e80a79bb7c4da0c8e /Documentation/hwmon/sysfs-interface
parentb04f2f7d387b3160883c2a1f5e2285483a791e82 (diff)
docs: hwmon: Add an index file and rename docs to *.rst
Now that all files were converted to ReST format, rename them and add an index. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
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-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.
-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.
-
-Note that motherboards vary widely in the 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
-before they make full sense. For example, most chips can only measure
-voltages between 0 and +4V. Other voltages are scaled back into that
-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
-values conversion, labeling of inputs and hiding of unused inputs.
-
-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
-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.
-
-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.
-
--------------------------------------------------------------------------
-
-======= ===========================================
-`[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
-======= ===========================================
-
-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.
-
-
-*****************
-Global attributes
-*****************
-
-`name`
- The chip name.
- This should be a short, lowercase string, not containing
- whitespace, dashes, or the wildcard character '*'.
- This attribute represents the chip name. It is the only
- mandatory attribute.
- I2C devices get this attribute created automatically.
-
- RO
-
-`update_interval`
- The interval at which the chip will update readings.
- Unit: millisecond
-
- RW
-
- Some devices have a variable update rate or interval.
- This attribute can be used to change it to the desired value.
-
-
-********
-Voltages
-********
-
-`in[0-*]_min`
- Voltage min value.
-
- Unit: millivolt
-
- RW
-
-`in[0-*]_lcrit`
- Voltage critical min value.
-
- Unit: millivolt
-
- RW
-
- If voltage drops to or below this limit, the system may
- take drastic action such as power down or reset. At the very
- least, it should report a fault.
-
-`in[0-*]_max`
- Voltage max value.
-
- Unit: millivolt
-
- RW
-
-`in[0-*]_crit`
- Voltage critical max value.
-
- Unit: millivolt
-
- RW
-
- If voltage reaches or exceeds this limit, the system may
- take drastic action such as power down or reset. At the very
- least, it should report a fault.
-
-`in[0-*]_input`
- Voltage input value.
-
- Unit: millivolt
-
- RO
-
- Voltage measured on the chip pin.
-
- Actual voltage depends on the scaling resistors on the
- motherboard, as recommended in the chip datasheet.
-
- This varies by chip and by motherboard.
- Because of this variation, values are generally NOT scaled
- by the chip driver, and must be done by the application.
- However, some drivers (notably lm87 and via686a)
- do scale, because of internal resistors built into a chip.
- These drivers will output the actual voltage. Rule of
- thumb: drivers should report the voltage values at the
- "pins" of the chip.
-
-`in[0-*]_average`
- Average voltage
-
- Unit: millivolt
-
- RO
-
-`in[0-*]_lowest`
- Historical minimum voltage
-
- Unit: millivolt
-
- RO
-
-`in[0-*]_highest`
- Historical maximum voltage
-
- Unit: millivolt
-
- RO
-
-`in[0-*]_reset_history`
- Reset inX_lowest and inX_highest
-
- WO
-
-`in_reset_history`
- Reset inX_lowest and inX_highest for all sensors
-
- WO
-
-`in[0-*]_label`
- Suggested voltage channel label.
-
- Text string
-
- Should only be created if the driver has hints about what
- this voltage channel is being used for, and user-space
- doesn't. In all other cases, the label is provided by
- user-space.
-
- RO
-
-`in[0-*]_enable`
- Enable or disable the sensors.
-
- When disabled the sensor read will return -ENODATA.
-
- - 1: Enable
- - 0: Disable
-
- RW
-
-`cpu[0-*]_vid`
- CPU core reference voltage.
-
- Unit: millivolt
-
- RO
-
- Not always correct.
-
-`vrm`
- Voltage Regulator Module version number.
-
- RW (but changing it should no more be necessary)
-
- Originally the VRM standard version multiplied by 10, but now
- an arbitrary number, as not all standards have a version
- number.
-
- Affects the way the driver calculates the CPU core reference
- voltage from the vid pins.
-
-Also see the Alarms section for status flags associated with voltages.
-
-
-****
-Fans
-****
-
-`fan[1-*]_min`
- Fan minimum value
-
- Unit: revolution/min (RPM)
-
- RW
-
-`fan[1-*]_max`
- Fan maximum value
-
- Unit: revolution/min (RPM)
-
- Only rarely supported by the hardware.
- RW
-
-`fan[1-*]_input`
- Fan input value.
-
- Unit: revolution/min (RPM)
-
- RO
-
-`fan[1-*]_div`
- Fan divisor.
-
- Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
-
- RW
-
- Some chips only support values 1, 2, 4 and 8.
- Note that this is actually an internal clock divisor, which
- affects the measurable speed range, not the read value.
-
-`fan[1-*]_pulses`
- Number of tachometer pulses per fan revolution.
-
- Integer value, typically between 1 and 4.
-
- RW
-
- This value is a characteristic of the fan connected to the
- device's input, so it has to be set in accordance with the fan
- model.
-
- Should only be created if the chip has a register to configure
- the number of pulses. In the absence of such a register (and
- thus attribute) the value assumed by all devices is 2 pulses
- per fan revolution.
-
-`fan[1-*]_target`
- Desired fan speed
-
- Unit: revolution/min (RPM)
-
- RW
-
- Only makes sense if the chip supports closed-loop fan speed
- control based on the measured fan speed.
-
-`fan[1-*]_label`
- Suggested fan channel label.
-
- Text string
-
- Should only be created if the driver has hints about what
- this fan channel is being used for, and user-space doesn't.
- In all other cases, the label is provided by user-space.
-
- RO
-
-`fan[1-*]_enable`
- Enable or disable the sensors.
-
- When disabled the sensor read will return -ENODATA.
-
- - 1: Enable
- - 0: Disable
-
- RW
-
-Also see the Alarms section for status flags associated with fans.
-
-
-***
-PWM
-***
-
-`pwm[1-*]`
- Pulse width modulation fan control.
-
- Integer value in the range 0 to 255
-
- RW
-
- 255 is max or 100%.
-
-`pwm[1-*]_enable`
- Fan speed control method:
-
- - 0: no fan speed control (i.e. fan at full speed)
- - 1: manual fan speed control enabled (using `pwm[1-*]`)
- - 2+: automatic fan speed control enabled
-
- Check individual chip documentation files for automatic mode
- details.
-
- RW
-
-`pwm[1-*]_mode`
- - 0: DC mode (direct current)
- - 1: PWM mode (pulse-width modulation)
-
- RW
-
-`pwm[1-*]_freq`
- Base PWM frequency in Hz.
-
- Only possibly available when pwmN_mode is PWM, but not always
- present even then.
-
- RW
-
-`pwm[1-*]_auto_channels_temp`
- Select which temperature channels affect this PWM output in
- auto mode.
-
- Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
- Which values are possible depend on the chip used.
-
- RW
-
-`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.
-
- Number of trip points is chip-dependent. Use this for chips
- which associate trip points to PWM output channels.
-
- RW
-
-`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.
-
- Number of trip points is chip-dependent. Use this for chips
- which associate trip points to temperature channels.
-
- RW
-
-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
-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.
-
- Integers 1 to 6
-
- RW
-
- - 1: CPU embedded diode
- - 2: 3904 transistor
- - 3: thermal diode
- - 4: thermistor
- - 5: AMD AMDSI
- - 6: Intel PECI
-
- Not all types are supported by all chips
-
-`temp[1-*]_max`
- Temperature max value.
-
- Unit: millidegree Celsius (or millivolt, see below)
-
- RW
-
-`temp[1-*]_min`
- Temperature min value.
-
- Unit: millidegree Celsius
-
- RW
-
-`temp[1-*]_max_hyst`
- Temperature hysteresis value for max limit.
-
- Unit: millidegree Celsius
-
- Must be reported as an absolute temperature, NOT a delta
- from the max value.
-
- RW
-
-`temp[1-*]_min_hyst`
- Temperature hysteresis value for min limit.
- Unit: millidegree Celsius
-
- Must be reported as an absolute temperature, NOT a delta
- from the min value.
-
- RW
-
-`temp[1-*]_input`
- Temperature input value.
-
- Unit: millidegree Celsius
-
- RO
-
-`temp[1-*]_crit`
- Temperature critical max value, typically greater than
- corresponding temp_max values.
-
- Unit: millidegree Celsius
-
- RW
-
-`temp[1-*]_crit_hyst`
- Temperature hysteresis value for critical limit.
-
- Unit: millidegree Celsius
-
- Must be reported as an absolute temperature, NOT a delta
- from the critical value.
-
- RW
-
-`temp[1-*]_emergency`
- Temperature emergency max value, for chips supporting more than
- two upper temperature limits. Must be equal or greater than
- corresponding temp_crit values.
-
- Unit: millidegree Celsius
-
- RW
-
-`temp[1-*]_emergency_hyst`
- Temperature hysteresis value for emergency limit.
-
- Unit: millidegree Celsius
-
- Must be reported as an absolute temperature, NOT a delta
- from the emergency value.
-
- RW
-
-`temp[1-*]_lcrit`
- Temperature critical min value, typically lower than
- corresponding temp_min values.
-
- Unit: millidegree Celsius
-
- RW
-
-`temp[1-*]_lcrit_hyst`
- Temperature hysteresis value for critical min limit.
-
- Unit: millidegree Celsius
-
- Must be reported as an absolute temperature, NOT a delta
- from the critical min value.
-
- RW
-
-`temp[1-*]_offset`
- Temperature offset which is added to the temperature reading
- by the chip.
-
- Unit: millidegree Celsius
-
- Read/Write value.
-
-`temp[1-*]_label`
- Suggested temperature channel label.
-
- Text string
-
- Should only be created if the driver has hints about what
- this temperature channel is being used for, and user-space
- doesn't. In all other cases, the label is provided by
- user-space.
-
- RO
-
-`temp[1-*]_lowest`
- Historical minimum temperature
-
- Unit: millidegree Celsius
-
- RO
-
-`temp[1-*]_highest`
- Historical maximum temperature
-
- Unit: millidegree Celsius
-
- RO
-
-`temp[1-*]_reset_history`
- Reset temp_lowest and temp_highest
-
- WO
-
-`temp_reset_history`
- Reset temp_lowest and temp_highest for all sensors
-
- WO
-
-`temp[1-*]_enable`
- Enable or disable the sensors.
-
- When disabled the sensor read will return -ENODATA.
-
- - 1: Enable
- - 0: Disable
-
- RW
-
-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
-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.
-
-
-********
-Currents
-********
-
-`curr[1-*]_max`
- Current max value
-
- Unit: milliampere
-
- RW
-
-`curr[1-*]_min`
- Current min value.
-
- Unit: milliampere
-
- RW
-
-`curr[1-*]_lcrit`
- Current critical low value
-
- Unit: milliampere
-
- RW
-
-`curr[1-*]_crit`
- Current critical high value.
-
- Unit: milliampere
-
- RW
-
-`curr[1-*]_input`
- Current input value
-
- Unit: milliampere
-
- RO
-
-`curr[1-*]_average`
- Average current use
-
- Unit: milliampere
-
- RO
-
-`curr[1-*]_lowest`
- Historical minimum current
-
- Unit: milliampere
-
- RO
-
-`curr[1-*]_highest`
- Historical maximum current
- Unit: milliampere
- RO
-
-`curr[1-*]_reset_history`
- Reset currX_lowest and currX_highest
-
- WO
-
-`curr_reset_history`
- Reset currX_lowest and currX_highest for all sensors
-
- WO
-
-`curr[1-*]_enable`
- Enable or disable the sensors.
-
- When disabled the sensor read will return -ENODATA.
-
- - 1: Enable
- - 0: Disable
-
- RW
-
-Also see the Alarms section for status flags associated with currents.
-
-*****
-Power
-*****
-
-`power[1-*]_average`
- Average power use
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_average_interval`
- Power use averaging interval. A poll
- notification is sent to this file if the
- hardware changes the averaging interval.
-
- Unit: milliseconds
-
- RW
-
-`power[1-*]_average_interval_max`
- Maximum power use averaging interval
-
- Unit: milliseconds
-
- RO
-
-`power[1-*]_average_interval_min`
- Minimum power use averaging interval
-
- Unit: milliseconds
-
- RO
-
-`power[1-*]_average_highest`
- Historical average maximum power use
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_average_lowest`
- Historical average minimum power use
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_average_max`
- A poll notification is sent to
- `power[1-*]_average` when power use
- rises above this value.
-
- Unit: microWatt
-
- RW
-
-`power[1-*]_average_min`
- A poll notification is sent to
- `power[1-*]_average` when power use
- sinks below this value.
-
- Unit: microWatt
-
- RW
-
-`power[1-*]_input`
- Instantaneous power use
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_input_highest`
- Historical maximum power use
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_input_lowest`
- Historical minimum power use
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_reset_history`
- Reset input_highest, input_lowest,
- average_highest and average_lowest.
-
- WO
-
-`power[1-*]_accuracy`
- Accuracy of the power meter.
-
- Unit: Percent
-
- RO
-
-`power[1-*]_cap`
- If power use rises above this limit, the
- system should take action to reduce power use.
- A poll notification is sent to this file if the
- cap is changed by the hardware. The `*_cap`
- files only appear if the cap is known to be
- enforced by hardware.
-
- Unit: microWatt
-
- RW
-
-`power[1-*]_cap_hyst`
- Margin of hysteresis built around capping and
- notification.
-
- Unit: microWatt
-
- RW
-
-`power[1-*]_cap_max`
- Maximum cap that can be set.
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_cap_min`
- Minimum cap that can be set.
-
- Unit: microWatt
-
- RO
-
-`power[1-*]_max`
- Maximum power.
-
- Unit: microWatt
-
- RW
-
-`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
-
-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
-
-********
-Humidity
-********
-
-`humidity[1-*]_input`
- Humidity
-
- Unit: milli-percent (per cent mille, pcm)
-
- RO
-
-
-`humidity[1-*]_enable`
- Enable or disable the sensors
-
- When disabled the sensor read will return
- -ENODATA.
-
- - 1: Enable
- - 0: Disable
-
- RW
-
-******
-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.
-
-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.
-
-`fan[1-*]_fault` / `temp[1-*]_fault`
- Input fault condition
-
- - 0: no fault occurred
- - 1: fault condition
-
- RO
-
-Some chips also offer the possibility to get beeped when an alarm occurs:
-
-`beep_enable`
- Master beep enable
-
- - 0: no beeps
- - 1: beeps
-
- RW
-
-`in[0-*]_beep`, `curr[1-*]_beep`, `fan[1-*]_beep`, `temp[1-*]_beep`,
- Channel beep
-
- - 0: disable
- - 1: enable
-
- RW
-
-In theory, a chip could provide per-limit beep masking, but no such chip
-was 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
-for compatibility reasons:
-
-`alarms`
- Alarm bitmask.
-
- RO
-
- Integer representation of one to four bytes.
-
- A '1' bit means an alarm.
-
- Chips should be programmed for 'comparator' mode so that
- the alarm will 'come back' after you read the register
- if it is still valid.
-
- Generally a direct representation of a chip's internal
- alarm registers; there is no standard for the position
- of individual bits. For this reason, the use of this
- interface file for new drivers is discouraged. Use
- `individual *_alarm` and `*_fault` files instead.
- Bits are defined in kernel/include/sensors.h.
-
-`beep_mask`
- Bitmask for beep.
- Same format as 'alarms' with the same bit locations,
- use discouraged for the same reason. Use individual
- `*_beep` files instead.
- RW
-
-
-*******************
-Intrusion detection
-*******************
-
-`intrusion[0-*]_alarm`
- Chassis intrusion detection
-
- - 0: OK
- - 1: intrusion detected
-
- RW
-
- Contrary to regular alarm flags which clear themselves
- automatically when read, this one sticks until cleared by
- the user. This is done by writing 0 to the file. Writing
- other values is unsupported.
-
-`intrusion[0-*]_beep`
- Chassis intrusion beep
-
- 0: disable
- 1: enable
-
- RW
-
-****************************
-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::
-
- unsigned long u = simple_strtoul(buf, NULL, 10);
- long s = simple_strtol(buf, NULL, 10);
-
-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);
-
- switch (v) {
- case 2: v = 1; break;
- case 4: v = 2; break;
- case 8: v = 3; break;
- default:
- return -EINVAL;
- }
- /* write v to register */