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diff --git a/Documentation/hwmon/adt7470 b/Documentation/hwmon/adt7470 new file mode 100644 index 000000000000..75d13ca147cc --- /dev/null +++ b/Documentation/hwmon/adt7470 @@ -0,0 +1,76 @@ +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 DOES NOT sample all inputs continuously. A single pin on the +ADT7470 is connected to a multitude of thermal diodes, but the chip must be +instructed explicitly to read the multitude of diodes. If you want to use +automatic fan control mode, you must manually read any of the temperature +sensors or the fan control algorithm will not run. The chip WILL NOT DO THIS +AUTOMATICALLY; this must be done from userspace. This may be a bug in the chip +design, given that many other AD chips take care of this. 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. + +Notes +----- + +As stated above, the temperature inputs must be read periodically from +userspace in order for the automatic pwm algorithm to run. |