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diff --git a/kernel/Documentation/hwmon/adt7475 b/kernel/Documentation/hwmon/adt7475 new file mode 100644 index 000000000..0502f2b46 --- /dev/null +++ b/kernel/Documentation/hwmon/adt7475 @@ -0,0 +1,117 @@ +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. |