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diff --git a/Documentation/hwmon/sysfs-interface.rst b/Documentation/hwmon/sysfs-interface.rst new file mode 100644 index 000000000..209626fb2 --- /dev/null +++ b/Documentation/hwmon/sysfs-interface.rst @@ -0,0 +1,656 @@ +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. + +Attribute access +---------------- + +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. + +------------------------------------------------------------------------- + +======= =========================================== +`[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. + +See Documentation/ABI/testing/sysfs-class-hwmon for a complete description +of the attributes. + +***************** +Global attributes +***************** + +`name` + The chip name. + +`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. + + +******** +Voltages +******** + +`in[0-*]_min` + Voltage min value. + +`in[0-*]_lcrit` + Voltage critical min value. + +`in[0-*]_max` + Voltage max value. + +`in[0-*]_crit` + Voltage critical max value. + +`in[0-*]_input` + Voltage input value. + +`in[0-*]_average` + Average voltage + +`in[0-*]_lowest` + Historical minimum voltage + +`in[0-*]_highest` + Historical maximum voltage + +`in[0-*]_reset_history` + Reset inX_lowest and inX_highest + +`in_reset_history` + Reset inX_lowest and inX_highest for all sensors + +`in[0-*]_label` + Suggested voltage channel label. + +`in[0-*]_enable` + Enable or disable the sensors. + +`cpu[0-*]_vid` + CPU core reference voltage. + +`vrm` + Voltage Regulator Module version number. + +`in[0-*]_rated_min` + Minimum rated voltage. + +`in[0-*]_rated_max` + Maximum rated voltage. + +Also see the Alarms section for status flags associated with voltages. + + +**** +Fans +**** + +`fan[1-*]_min` + Fan minimum value + +`fan[1-*]_max` + Fan maximum value + +`fan[1-*]_input` + Fan input value. + +`fan[1-*]_div` + Fan divisor. + +`fan[1-*]_pulses` + Number of tachometer pulses per fan revolution. + +`fan[1-*]_target` + Desired fan speed + +`fan[1-*]_label` + Suggested fan channel label. + +`fan[1-*]_enable` + Enable or disable the sensors. + +Also see the Alarms section for status flags 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 +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. + +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. + +`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. + +`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. + +`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 + +******** +Humidity +******** + +`humidity[1-*]_input` + Humidity. + +`humidity[1-*]_enable` + Enable or disable the sensors. + +`humidity[1-*]_rated_min` + Minimum rated humidity. + +`humidity[1-*]_rated_max` + Maximum rated humidity. + +****** +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. + +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. + +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. + +`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:: + + 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 */ |