Kernel driver NCT6775
  =====================

  .. note::
  
      This driver supersedes the NCT6775F and NCT6776F support in the W83627EHF
      driver.

  Supported chips:

    * Nuvoton NCT6102D/NCT6104D/NCT6106D

      Prefix: 'nct6106'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from the Nuvoton web site

    * Nuvoton NCT5572D/NCT6771F/NCT6772F/NCT6775F/W83677HG-I

      Prefix: 'nct6775'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT5573D/NCT5577D/NCT6776D/NCT6776F

      Prefix: 'nct6776'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT5532D/NCT6779D

      Prefix: 'nct6779'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT6791D

      Prefix: 'nct6791'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT6792D

      Prefix: 'nct6792'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT6793D

      Prefix: 'nct6793'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT6795D

      Prefix: 'nct6795'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

    * Nuvoton NCT6796D

      Prefix: 'nct6796'

      Addresses scanned: ISA address retrieved from Super I/O registers

      Datasheet: Available from Nuvoton upon request

  Authors:

  
  	Guenter Roeck <linux@roeck-us.net>

  
  Description
  -----------
  
  This driver implements support for the Nuvoton NCT6775F, NCT6776F, and NCT6779D

  and compatible super I/O chips.

  
  The chips support up to 25 temperature monitoring sources. Up to 6 of those are
  direct temperature sensor inputs, the others are special sources such as PECI,
  PCH, and SMBUS. Depending on the chip type, 2 to 6 of the temperature sources
  can be monitored and compared against minimum, maximum, and critical
  temperatures. The driver reports up to 10 of the temperatures to the user.
  There are 4 to 5 fan rotation speed sensors, 8 to 15 analog voltage sensors,
  one VID, alarms with beep warnings (control unimplemented), and some automatic
  fan regulation strategies (plus manual fan control mode).
  
  The temperature sensor sources on all chips are configurable. The configured
  source for each of the temperature sensors is provided in tempX_label.
  
  Temperatures are measured in degrees Celsius and measurement resolution is
  either 1 degC or 0.5 degC, depending on the temperature source and
  configuration. An alarm is triggered when the temperature gets higher than
  the high limit; it stays on until the temperature falls below the hysteresis
  value. Alarms are only supported for temp1 to temp6, depending on the chip type.
  
  Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
  triggered if the rotation speed has dropped below a programmable limit. On
  NCT6775F, fan readings can be divided by a programmable divider (1, 2, 4, 8,
  16, 32, 64 or 128) to give the readings more range or accuracy; the other chips
  do not have a fan speed divider. The driver sets the most suitable fan divisor

  itself; specifically, it increases the divider value each time a fan speed
  reading returns an invalid value, and it reduces it if the fan speed reading
  is lower than optimal. Some fans might not be present because they share pins

  with other functions.
  
  Voltage sensors (also known as IN sensors) report their values in millivolts.
  An alarm is triggered if the voltage has crossed a programmable minimum
  or maximum limit.
  
  The driver supports automatic fan control mode known as Thermal Cruise.
  In this mode, the chip attempts to keep the measured temperature in a
  predefined temperature range. If the temperature goes out of range, fan
  is driven slower/faster to reach the predefined range again.
  
  The mode works for fan1-fan5.

  sysfs attributes
  ----------------

  pwm[1-7]
      - this file stores PWM duty cycle or DC value (fan speed) in range:

  	   0 (lowest speed) to 255 (full)

  pwm[1-7]_enable
      - this file controls mode of fan/temperature control:

  	* 0 Fan control disabled (fans set to maximum speed)
  	* 1 Manual mode, write to pwm[0-5] any value 0-255
  	* 2 "Thermal Cruise" mode
  	* 3 "Fan Speed Cruise" mode
  	* 4 "Smart Fan III" mode (NCT6775F only)
  	* 5 "Smart Fan IV" mode

  pwm[1-7]_mode
      - controls if output is PWM or DC level
  
  	* 0 DC output
  	* 1 PWM output

  Common fan control attributes
  -----------------------------

  pwm[1-7]_temp_sel
  			Temperature source. Value is temperature sensor index.

  			For example, select '1' for temp1_input.

  pwm[1-7]_weight_temp_sel

  			Secondary temperature source. Value is temperature
  			sensor index. For example, select '1' for temp1_input.
  			Set to 0 to disable secondary temperature control.
  
  If secondary temperature functionality is enabled, it is controlled with the
  following attributes.

  pwm[1-7]_weight_duty_step

  			Duty step size.

  pwm[1-7]_weight_temp_step

  			Temperature step size. With each step over
  			temp_step_base, the value of weight_duty_step is added
  			to the current pwm value.

  pwm[1-7]_weight_temp_step_base

  			Temperature at which secondary temperature control kicks
  			in.

  pwm[1-7]_weight_temp_step_tol

  			Temperature step tolerance.

  
  Thermal Cruise mode (2)
  -----------------------
  
  If the temperature is in the range defined by:

  pwm[1-7]_target_temp
  			Target temperature, unit millidegree Celsius

  			(range 0 - 127000)

  pwm[1-7]_temp_tolerance

  			Target temperature tolerance, unit millidegree Celsius

  There are no changes to fan speed. Once the temperature leaves the interval, fan

  speed increases (if temperature is higher that desired) or decreases (if
  temperature is lower than desired), using the following limits and time
  intervals.

  pwm[1-7]_start
  			fan pwm start value (range 1 - 255), to start fan

  			when the temperature is above defined range.

  
  pwm[1-7]_floor
  			lowest fan pwm (range 0 - 255) if temperature is below

  			the defined range. If set to 0, the fan is expected to
  			stop if the temperature is below the defined range.

  
  pwm[1-7]_step_up_time
  			milliseconds before fan speed is increased
  
  pwm[1-7]_step_down_time
  			milliseconds before fan speed is decreased
  
  pwm[1-7]_stop_time
  			how many milliseconds must elapse to switch

  			corresponding fan off (when the temperature was below
  			defined range).
  
  Speed Cruise mode (3)
  ---------------------
  
  This modes tries to keep the fan speed constant.

  fan[1-7]_target
  			Target fan speed

  fan[1-7]_tolerance

  			Target speed tolerance
  
  
  Untested; use at your own risk.
  
  Smart Fan IV mode (5)
  ---------------------
  
  This mode offers multiple slopes to control the fan speed. The slopes can be
  controlled by setting the pwm and temperature attributes. When the temperature
  rises, the chip will calculate the DC/PWM output based on the current slope.
  There are up to seven data points depending on the chip type. Subsequent data
  points should be set to higher temperatures and higher pwm values to achieve
  higher fan speeds with increasing temperature. The last data point reflects
  critical temperature mode, in which the fans should run at full speed.

  pwm[1-7]_auto_point[1-7]_pwm

  			pwm value to be set if temperature reaches matching
  			temperature range.

  pwm[1-7]_auto_point[1-7]_temp

  			Temperature over which the matching pwm is enabled.

  pwm[1-7]_temp_tolerance

  			Temperature tolerance, unit millidegree Celsius

  pwm[1-7]_crit_temp_tolerance

  			Temperature tolerance for critical temperature,
  			unit millidegree Celsius

  pwm[1-7]_step_up_time
  			milliseconds before fan speed is increased
  
  pwm[1-7]_step_down_time
  			milliseconds before fan speed is decreased

  Usage Notes
  -----------
  
  On various ASUS boards with NCT6776F, it appears that CPUTIN is not really
  connected to anything and floats, or that it is connected to some non-standard
  temperature measurement device. As a result, the temperature reported on CPUTIN
  will not reflect a usable value. It often reports unreasonably high
  temperatures, and in some cases the reported temperature declines if the actual
  temperature increases (similar to the raw PECI temperature value - see PECI

  specification for details). CPUTIN should therefore be ignored on ASUS

  boards. The CPU temperature on ASUS boards is reported from PECI 0.