Add at least the bare minimum of documentation for this chip. Signed-off-by: Darrick J. Wong <djwong at us.ibm.com> --- Documentation/hwmon/adt7470 | 74 +++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 74 insertions(+), 0 deletions(-) diff --git a/Documentation/hwmon/adt7470 b/Documentation/hwmon/adt7470 new file mode 100644 index 0000000..10f398b --- /dev/null +++ b/Documentation/hwmon/adt7470 @@ -0,0 +1,74 @@ +Kernel driver adt7470 +====================== + +Supported chips: + * Analog Devices ADT7470 + Prefix: 'adt7470' + Addresses scanned: I2C 0x2C, 0x2E, 0x2F + Datasheet: Publicly available at the Analog Devices website + +Author: Darrick J. Wong + +Description +----------- + +This driver implements support for the Analog Devices ADT7470 chip family. + +The ADT7470 uses the 2-wire interface compatible with the SMBUS 2.0 +specification. Using an analog to digital converter it measures ten (10) +temperatures. It has four (4) 16-bit counters for measuring fan speed. There +are four (4) PWM outputs that can be used to control fan speed. + +A sophisticated control system for the PWM outputs is designed into the ADT7470 +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 ADT7470 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 (temperature, fan speed) has corresponding high/low +limit values. The ADT7470 will signal an ALARM if any measured value exceeds +either limit. + +The ADT7470 DOES NOT sample all inputs continuously. A single pin on the +ADT7470 is connected to a multitude of thermal diodes, but the chip must be +instructed explicitly to read the multitude of diodes. If you want to use +automatic fan control mode, you must manually read any of the temperature +sensors or the fan control algorithm will not run. The chip WILL NOT DO THIS +AUTOMATICALLY; this must be done from userspace. This may be a bug in the chip +design, given that many other AD chips take care of this. 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 ADT7470 have a 8-bit ADC and can therefore measure temperatures +with 1 degC resolution. + +The Analog Devices datasheet is very detailed and describes a procedure for +determining an optimal configuration for the automatic PWM control. + +Configuration Notes +------------------- + +Besides standard interfaces driver adds the following: + +* PWM Control + +* pwm#_auto_point1_pwm and temp#_auto_point1_temp and +* pwm#_auto_point2_pwm and temp#_auto_point2_temp - + +point1: Set the pwm speed at a lower temperature bound. +point2: Set the pwm speed at a higher temperature bound. + +The ADT7470 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). Fan speed will be set to maximum when the +temperature sensor associated with the PWM control exceeds temp#_max. + +Notes +----- + +As stated above, the temperature inputs must be read periodically from +userspace in order for the automatic pwm algorithm to run.
