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diff --git a/Documentation/hwmon/adt7470.rst b/Documentation/hwmon/adt7470.rst new file mode 100644 index 000000000000..d225f816e992 --- /dev/null +++ b/Documentation/hwmon/adt7470.rst @@ -0,0 +1,94 @@ +Kernel driver adt7470 +===================== + +Supported chips: + + * Analog Devices ADT7470 + + Prefix: 'adt7470' + + Addresses scanned: I2C 0x2C, 0x2E, 0x2F + + Datasheet: Publicly available at the Analog Devices website + +Author: Darrick J. Wong + +Description +----------- + +This driver implements support for the Analog Devices ADT7470 chip. There may +be other chips that implement this interface. + +The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0 +specification. Using an analog to digital converter it measures up to ten (10) +external temperatures. It has four (4) 16-bit counters for measuring fan speed. +There are four (4) PWM outputs that can be used to control fan speed. + +A sophisticated control system for the PWM outputs is designed into the ADT7470 +that allows fan speed to be adjusted automatically based on any of the ten +temperature sensors. Each PWM output is individually adjustable and +programmable. Once configured, the ADT7470 will adjust the PWM outputs in +response to the measured temperatures with further host intervention. This +feature can also be disabled for manual control of the PWM's. + +Each of the measured inputs (temperature, fan speed) has corresponding high/low +limit values. The ADT7470 will signal an ALARM if any measured value exceeds +either limit. + +The ADT7470 samples all inputs continuously. A kernel thread is started up for +the purpose of periodically querying the temperature sensors, thus allowing the +automatic fan pwm control to set the fan speed. The driver will not read the +registers more often than once every 5 seconds. Further, configuration data is +only read once per minute. + +Special Features +---------------- + +The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1 +degC resolution. + +The Analog Devices datasheet is very detailed and describes a procedure for +determining an optimal configuration for the automatic PWM control. + +Configuration Notes +------------------- + +Besides standard interfaces driver adds the following: + +* PWM Control + +* pwm#_auto_point1_pwm and pwm#_auto_point1_temp and +* pwm#_auto_point2_pwm and pwm#_auto_point2_temp - + + - point1: Set the pwm speed at a lower temperature bound. + - point2: Set the pwm speed at a higher temperature bound. + +The ADT7470 will scale the pwm between the lower and higher pwm speed when +the temperature is between the two temperature boundaries. PWM values range +from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the +temperature sensor associated with the PWM control exceeds +pwm#_auto_point2_temp. + +The driver also allows control of the PWM frequency: + +* pwm1_freq + +The PWM frequency is rounded to the nearest one of: + +* 11.0 Hz +* 14.7 Hz +* 22.1 Hz +* 29.4 Hz +* 35.3 Hz +* 44.1 Hz +* 58.8 Hz +* 88.2 Hz +* 1.4 kHz +* 22.5 kHz + +Notes +----- + +The temperature inputs no longer need to be read periodically from userspace in +order for the automatic pwm algorithm to run. This was the case for earlier +versions of the driver. |