[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / hwmon / adt7470

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.  There may
be other chips that implement this interface.

The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
specification. Using an analog to digital converter it measures up to ten (10)
external 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 ten
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 with 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 samples all inputs continuously.  A kernel thread is started up for
the purpose of periodically querying the temperature sensors, thus allowing the
automatic fan pwm control to set the fan speed.  The driver will not read the
registers more often than once every 5 seconds.  Further, configuration data is
only read once per minute.

Special Features
----------------

The ADT7470 has a 8-bit ADC and is capable of measuring 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 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 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
pwm#_auto_point2_temp.

Notes
-----

The temperature inputs no longer need to be read periodically from userspace in
order for the automatic pwm algorithm to run.  This was the case for earlier
versions of the driver.
Commit	Line	Data
d664a480 DW	1	Kernel driver adt7470
	2	=====================
	3
	4	Supported chips:
	5	* Analog Devices ADT7470
	6	Prefix: 'adt7470'
	7	Addresses scanned: I2C 0x2C, 0x2E, 0x2F
	8	Datasheet: Publicly available at the Analog Devices website
	9
	10	Author: Darrick J. Wong
	11
	12	Description
	13	-----------
	14
	15	This driver implements support for the Analog Devices ADT7470 chip. There may
	16	be other chips that implement this interface.
	17
	18	The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
	19	specification. Using an analog to digital converter it measures up to ten (10)
	20	external temperatures. It has four (4) 16-bit counters for measuring fan speed.
	21	There are four (4) PWM outputs that can be used to control fan speed.
	22
	23	A sophisticated control system for the PWM outputs is designed into the ADT7470
	24	that allows fan speed to be adjusted automatically based on any of the ten
	25	temperature sensors. Each PWM output is individually adjustable and
	26	programmable. Once configured, the ADT7470 will adjust the PWM outputs in
	27	response to the measured temperatures with further host intervention. This
	28	feature can also be disabled for manual control of the PWM's.
	29
	30	Each of the measured inputs (temperature, fan speed) has corresponding high/low
	31	limit values. The ADT7470 will signal an ALARM if any measured value exceeds
	32	either limit.
	33
89fac11c DW	34	The ADT7470 samples all inputs continuously. A kernel thread is started up for
	35	the purpose of periodically querying the temperature sensors, thus allowing the
	36	automatic fan pwm control to set the fan speed. The driver will not read the
	37	registers more often than once every 5 seconds. Further, configuration data is
	38	only read once per minute.
d664a480 DW	39
	40	Special Features
	41	----------------
	42
	43	The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1
	44	degC resolution.
	45
	46	The Analog Devices datasheet is very detailed and describes a procedure for
	47	determining an optimal configuration for the automatic PWM control.
	48
	49	Configuration Notes
	50	-------------------
	51
	52	Besides standard interfaces driver adds the following:
	53
	54	* PWM Control
	55
	56	* pwm#_auto_point1_pwm and pwm#_auto_point1_temp and
	57	* pwm#_auto_point2_pwm and pwm#_auto_point2_temp -
	58
	59	point1: Set the pwm speed at a lower temperature bound.
	60	point2: Set the pwm speed at a higher temperature bound.
	61
	62	The ADT7470 will scale the pwm between the lower and higher pwm speed when
	63	the temperature is between the two temperature boundaries. PWM values range
	64	from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the
	65	temperature sensor associated with the PWM control exceeds
	66	pwm#_auto_point2_temp.
	67
	68	Notes
	69	-----
	70
89fac11c DW	71	The temperature inputs no longer need to be read periodically from userspace in
	72	order for the automatic pwm algorithm to run. This was the case for earlier
	73	versions of the driver.