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Documentation/hwmon/sysfs-interface
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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 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 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 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 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 Also see the Alarms section for status flags associated with power readings. ********** * Energy * ********** energy[1-*]_input Cumulative energy use Unit: microJoule RO ************ * Humidity * ************ humidity[1-*]_input Humidity Unit: milli-percent (per cent mille, pcm) RO ********** * 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 curr[1-*]_alarm power[1-*]_alarm fan[1-*]_alarm temp[1-*]_alarm Channel alarm 0: no alarm 1: alarm RO OR in[0-*]_min_alarm 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-*]_crit_alarm temp[1-*]_emergency_alarm Limit alarm 0: no alarm 1: alarm RO 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 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 */ |