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d664a4809e
Add at least the bare minimum of documentation for this chip. Signed-off-by: Darrick J. Wong <djwong@us.ibm.com> Signed-off-by: Jean Delvare <khali@linux-fr.org>
77 lines
2.9 KiB
Plaintext
77 lines
2.9 KiB
Plaintext
Kernel driver adt7470
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=====================
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Supported chips:
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* Analog Devices ADT7470
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Prefix: 'adt7470'
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Addresses scanned: I2C 0x2C, 0x2E, 0x2F
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Datasheet: Publicly available at the Analog Devices website
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Author: Darrick J. Wong
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Description
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-----------
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This driver implements support for the Analog Devices ADT7470 chip. There may
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be other chips that implement this interface.
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The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
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specification. Using an analog to digital converter it measures up to ten (10)
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external temperatures. It has four (4) 16-bit counters for measuring fan speed.
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There are four (4) PWM outputs that can be used to control fan speed.
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A sophisticated control system for the PWM outputs is designed into the ADT7470
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that allows fan speed to be adjusted automatically based on any of the ten
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temperature sensors. Each PWM output is individually adjustable and
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programmable. Once configured, the ADT7470 will adjust the PWM outputs in
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response to the measured temperatures with further host intervention. This
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feature can also be disabled for manual control of the PWM's.
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Each of the measured inputs (temperature, fan speed) has corresponding high/low
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limit values. The ADT7470 will signal an ALARM if any measured value exceeds
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either limit.
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The ADT7470 DOES NOT sample all inputs continuously. A single pin on the
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ADT7470 is connected to a multitude of thermal diodes, but the chip must be
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instructed explicitly to read the multitude of diodes. If you want to use
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automatic fan control mode, you must manually read any of the temperature
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sensors or the fan control algorithm will not run. The chip WILL NOT DO THIS
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AUTOMATICALLY; this must be done from userspace. This may be a bug in the chip
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design, given that many other AD chips take care of this. The driver will not
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read the registers more often than once every 5 seconds. Further,
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configuration data is only read once per minute.
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Special Features
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----------------
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The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1
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degC resolution.
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The Analog Devices datasheet is very detailed and describes a procedure for
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determining an optimal configuration for the automatic PWM control.
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Configuration Notes
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-------------------
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Besides standard interfaces driver adds the following:
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* PWM Control
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* pwm#_auto_point1_pwm and pwm#_auto_point1_temp and
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* pwm#_auto_point2_pwm and pwm#_auto_point2_temp -
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point1: Set the pwm speed at a lower temperature bound.
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point2: Set the pwm speed at a higher temperature bound.
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The ADT7470 will scale the pwm between the lower and higher pwm speed when
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the temperature is between the two temperature boundaries. PWM values range
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from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the
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temperature sensor associated with the PWM control exceeds
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pwm#_auto_point2_temp.
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Notes
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-----
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As stated above, the temperature inputs must be read periodically from
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userspace in order for the automatic pwm algorithm to run.
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