Kernel driver adt7475
  =====================
  
  Supported chips:
    * Analog Devices ADT7473
      Prefix: 'adt7473'
      Addresses scanned: I2C 0x2C, 0x2D, 0x2E
      Datasheet: Publicly available at the On Semiconductors website
    * Analog Devices ADT7475
      Prefix: 'adt7475'
      Addresses scanned: I2C 0x2E
      Datasheet: Publicly available at the On Semiconductors website

    * Analog Devices ADT7476
      Prefix: 'adt7476'
      Addresses scanned: I2C 0x2C, 0x2D, 0x2E
      Datasheet: Publicly available at the On Semiconductors website

    * Analog Devices ADT7490
      Prefix: 'adt7490'
      Addresses scanned: I2C 0x2C, 0x2D, 0x2E
      Datasheet: Publicly available at the On Semiconductors website

  
  Authors:
  	Jordan Crouse
  	Hans de Goede
  	Darrick J. Wong (documentation)

  	Jean Delvare

  
  
  Description
  -----------

  This driver implements support for the Analog Devices ADT7473, ADT7475,
  ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in
  minor details. The ADT7476 has additional features, including extra voltage
  measurement inputs and VID support. The ADT7490 also has additional
  features, including extra voltage measurement inputs and PECI support. All
  the supported chips will be collectively designed by the name "ADT747x" in
  the rest of this document.

  
  The ADT747x uses the 2-wire interface compatible with the SMBus 2.0
  specification. Using an analog to digital converter it measures three (3)

  temperatures and two (2) or more voltages. It has four (4) 16-bit counters
  for measuring fan speed. There are three (3) PWM outputs that can be used

  to control fan speed.
  
  A sophisticated control system for the PWM outputs is designed into the
  ADT747x that allows fan speed to be adjusted automatically based on any of the
  three temperature sensors. Each PWM output is individually adjustable and
  programmable. Once configured, the ADT747x will adjust the PWM outputs in
  response to the measured temperatures without further host intervention.
  This feature can also be disabled for manual control of the PWM's.
  
  Each of the measured inputs (voltage, temperature, fan speed) has
  corresponding high/low limit values. The ADT747x will signal an ALARM if
  any measured value exceeds either limit.
  
  The ADT747x samples all inputs continuously. The driver will not read
  the registers more often than once every other second. Further,
  configuration data is only read once per minute.

  Chip Differences Summary
  ------------------------
  
  ADT7473:
    * 2 voltage inputs
    * system acoustics optimizations (not implemented)
  
  ADT7475:
    * 2 voltage inputs

  ADT7476:
    * 5 voltage inputs

    * VID support

  ADT7490:
    * 6 voltage inputs
    * 1 Imon input (not implemented)
    * PECI support (not implemented)
    * 2 GPIO pins (not implemented)
    * system acoustics optimizations (not implemented)

  Special Features
  ----------------
  
  The ADT747x has a 10-bit ADC and can therefore measure temperatures
  with a resolution of 0.25 degree Celsius. Temperature readings can be
  configured either for two's complement format or "Offset 64" format,
  wherein 64 is subtracted from the raw value to get the temperature value.
  
  The datasheet is very detailed and describes a procedure for determining
  an optimal configuration for the automatic PWM control.
  
  Fan Speed Control
  -----------------
  
  The driver exposes two trip points per PWM channel.
  
  point1: Set the PWM speed at the lower temperature bound
  point2: Set the PWM speed at the higher temperature bound
  
  The ADT747x will scale the PWM linearly between the lower and higher PWM
  speed when the temperature is between the two temperature boundaries.
  Temperature boundaries are associated to temperature channels rather than
  PWM outputs, and a given PWM output can be controlled by several temperature
  channels. As a result, the ADT747x may compute more than one PWM value
  for a channel at a given time, in which case the maximum value (fastest
  fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
  
  Fan speed may be set to maximum when the temperature sensor associated with
  the PWM control exceeds temp#_max.
  
  Notes
  -----
  
  The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.
  Unfortunately, they fail to set the i2c adapter class, so this driver may
  fail to find the chip until the nvidia driver is patched.