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diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface new file mode 100644 index 0000000..6dbfd5e --- /dev/null +++ b/Documentation/hwmon/sysfs-interface @@ -0,0 +1,505 @@ +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 +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. + + +******** +* Name * +******** + +name The chip name. + This should be a short, lowercase string, not containing + spaces nor dashes, representing the chip name. This is + the only mandatory attribute. + I2C devices get this attribute created automatically. + RO + + +************ +* Voltages * +************ + +in[0-*]_min Voltage min value. + Unit: millivolt + RW + +in[0-*]_max Voltage max value. + Unit: millivolt + RW + +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-*]_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-*]_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-*]_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 + +OR + +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 + + +**************** +* Temperatures * +**************** + +temp[1-*]_type Sensor type selection. + Integers 1 to 6 + RW + 1: PII/Celeron 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-*]_input Temperature input value. + Unit: millidegree Celsius + RO + +temp[1-*]_crit Temperature critical 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-*]_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 + +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 * +************ + +Note that no known chip provides current measurements as of writing, +so this part is theoretical, so to say. + +curr[1-*]_max Current max value + Unit: milliampere + RW + +curr[1-*]_min Current min value. + Unit: milliampere + RW + +curr[1-*]_input Current input value + Unit: milliampere + RO + +********* +* Power * +********* + +power[1-*]_average Average power use + Unit: microWatt + RO + +power[1-*]_average_interval Power use averaging interval + Unit: milliseconds + RW + +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-*]_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 + +********** +* Energy * +********** + +energy[1-*]_input Cumulative energy use + Unit: microJoule + 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 +fan[1-*]_alarm +temp[1-*]_alarm + Channel alarm + 0: no alarm + 1: alarm + RO + +OR + +in[0-*]_min_alarm +in[0-*]_max_alarm +fan[1-*]_min_alarm +temp[1-*]_min_alarm +temp[1-*]_max_alarm +temp[1-*]_crit_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. + +in[0-*]_fault +fan[1-*]_fault +temp[1-*]_fault + Input fault condition + 0: no fault occured + 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 +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 + + +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 SENSORS_LIMIT(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 = SENSORS_LIMIT(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 */ |
