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-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.