hwmon: New driver for Analog Devices ADT7473 sensor chip

This driver reports voltage, temperature and fan sensor readings
on an ADT7473 chip.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>

1 files changed, 79 insertions, 0 deletions

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+Kernel driver adt7473
+======================
+
+Supported chips:
+  * Analog Devices ADT7473
+    Prefix: 'adt7473'
+    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
+    Datasheet: Publicly available at the Analog Devices website
+
+Author: Darrick J. Wong
+
+Description
+-----------
+
+This driver implements support for the Analog Devices ADT7473 chip family.
+
+The LM85 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) voltages. It has three (3) 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
+LM85 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 ADT7473 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 ADT7473 will signal an ALARM if
+any measured value exceeds either limit.
+
+The ADT7473 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.
+
+Special Features
+----------------
+
+The ADT7473 have a 10-bit ADC and can therefore measure temperatures
+with 0.25 degC resolution. Temperature readings can be configured either
+for twos complement format or "Offset 64" format, wherein 63 is subtracted
+from the raw value to get the temperature value.
+
+The Analog Devices datasheet is very detailed and describes a procedure for
+determining an optimal configuration for the automatic PWM control.
+
+Hardware Configurations
+-----------------------
+
+The ADT7473 chips have an optional SMBALERT output that can be used to
+signal the chipset in case a limit is exceeded or the temperature sensors
+fail. Individual sensor interrupts can be masked so they won't trigger
+SMBALERT. The SMBALERT output if configured replaces the PWM2 function.
+
+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 ADT7473 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).
+
+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.