Kernel driver it87
  ==================
  
  Supported chips:
    * IT8705F
      Prefix: 'it87'

      Addresses scanned: from Super I/O config space (8 I/O ports)

      Datasheet: Once publicly available at the ITE website, but no longer

    * IT8712F
      Prefix: 'it8712'

      Addresses scanned: from Super I/O config space (8 I/O ports)

      Datasheet: Once publicly available at the ITE website, but no longer

    * IT8716F/IT8726F

      Prefix: 'it8716'
      Addresses scanned: from Super I/O config space (8 I/O ports)

      Datasheet: Once publicly available at the ITE website, but no longer

    * IT8718F
      Prefix: 'it8718'
      Addresses scanned: from Super I/O config space (8 I/O ports)

      Datasheet: Once publicly available at the ITE website, but no longer

    * IT8720F
      Prefix: 'it8720'
      Addresses scanned: from Super I/O config space (8 I/O ports)

      Datasheet: Not publicly available

    * IT8721F/IT8758E
      Prefix: 'it8721'
      Addresses scanned: from Super I/O config space (8 I/O ports)
      Datasheet: Not publicly available

    * IT8728F
      Prefix: 'it8728'
      Addresses scanned: from Super I/O config space (8 I/O ports)
      Datasheet: Not publicly available

    * SiS950   [clone of IT8705F]

      Prefix: 'it87'
      Addresses scanned: from Super I/O config space (8 I/O ports)

      Datasheet: No longer be available

  Authors:

      Christophe Gauthron

      Jean Delvare <khali@linux-fr.org>

  
  
  Module Parameters
  -----------------
  
  * update_vbat: int
  
    0 if vbat should report power on value, 1 if vbat should be updated after
    each read. Default is 0. On some boards the battery voltage is provided
    by either the battery or the onboard power supply. Only the first reading
    at power on will be the actual battery voltage (which the chip does
    automatically). On other boards the battery voltage is always fed to
    the chip so can be read at any time. Excessive reading may decrease
    battery life but no information is given in the datasheet.
  
  * fix_pwm_polarity int
  
    Force PWM polarity to active high (DANGEROUS). Some chips are
    misconfigured by BIOS - PWM values would be inverted. This option tries
    to fix this. Please contact your BIOS manufacturer and ask him for fix.

  
  Hardware Interfaces
  -------------------
  
  All the chips suported by this driver are LPC Super-I/O chips, accessed
  through the LPC bus (ISA-like I/O ports). The IT8712F additionally has an
  SMBus interface to the hardware monitoring functions. This driver no
  longer supports this interface though, as it is slower and less reliable
  than the ISA access, and was only available on a small number of
  motherboard models.

  Description
  -----------

  This driver implements support for the IT8705F, IT8712F, IT8716F,

  IT8718F, IT8720F, IT8721F, IT8726F, IT8728F, IT8758E and SiS950 chips.

  
  These chips are 'Super I/O chips', supporting floppy disks, infrared ports,
  joysticks and other miscellaneous stuff. For hardware monitoring, they
  include an 'environment controller' with 3 temperature sensors, 3 fan

  rotation speed sensors, 8 voltage sensors, associated alarms, and chassis
  intrusion detection.

  The IT8712F and IT8716F additionally feature VID inputs, used to report
  the Vcore voltage of the processor. The early IT8712F have 5 VID pins,
  the IT8716F and late IT8712F have 6. They are shared with other functions
  though, so the functionality may not be available on a given system.

  The IT8718F and IT8720F also features VID inputs (up to 8 pins) but the value
  is stored in the Super-I/O configuration space. Due to technical limitations,

  this value can currently only be read once at initialization time, so
  the driver won't notice and report changes in the VID value. The two
  upper VID bits share their pins with voltage inputs (in5 and in6) so you
  can't have both on a given board.

  The IT8716F, IT8718F, IT8720F, IT8721F/IT8758E and later IT8712F revisions
  have support for 2 additional fans. The additional fans are supported by the
  driver.

  The IT8716F, IT8718F, IT8720F and IT8721F/IT8758E, and late IT8712F and
  IT8705F also have optional 16-bit tachometer counters for fans 1 to 3. This
  is better (no more fan clock divider mess) but not compatible with the older
  chips and revisions. The 16-bit tachometer mode is enabled by the driver when
  one of the above chips is detected.

  The IT8726F is just bit enhanced IT8716F with additional hardware
  for AMD power sequencing. Therefore the chip will appear as IT8716F
  to userspace applications.

  The IT8728F is considered compatible with the IT8721F, until a datasheet
  becomes available (hopefully.)

  Temperatures are measured in degrees Celsius. An alarm is triggered once
  when the Overtemperature Shutdown limit is crossed.
  
  Fan rotation speeds are reported in RPM (rotations per minute). An alarm is

  triggered if the rotation speed has dropped below a programmable limit. When
  16-bit tachometer counters aren't used, fan readings can be divided by
  a programmable divider (1, 2, 4 or 8) to give the readings more range or
  accuracy. With a divider of 2, the lowest representable value is around
  2600 RPM. Not all RPM values can accurately be represented, so some rounding
  is done.

  
  Voltage sensors (also known as IN sensors) report their values in volts. An
  alarm is triggered if the voltage has crossed a programmable minimum or
  maximum limit. Note that minimum in this case always means 'closest to
  zero'; this is important for negative voltage measurements. All voltage
  inputs can measure voltages between 0 and 4.08 volts, with a resolution of

  0.016 volt (except IT8721F/IT8758E and IT8728F: 0.012 volt.) The battery
  voltage in8 does not have limit registers.

  
  On the IT8721F/IT8758E, some voltage inputs are internal and scaled inside
  the chip (in7, in8 and optionally in3). The driver handles this transparently
  so user-space doesn't have to care.

  The VID lines (IT8712F/IT8716F/IT8718F/IT8720F) encode the core voltage value:

  the voltage level your processor should work with. This is hardcoded by
  the mainboard and/or processor itself. It is a value in volts.

  
  If an alarm triggers, it will remain triggered until the hardware register
  is read at least once. This means that the cause for the alarm may already
  have disappeared! Note that in the current implementation, all hardware
  registers are read whenever any data is read (unless it is less than 1.5
  seconds since the last update). This means that you can easily miss
  once-only alarms.

  Out-of-limit readings can also result in beeping, if the chip is properly
  wired and configured. Beeping can be enabled or disabled per sensor type
  (temperatures, voltages and fans.)

  The IT87xx only updates its values each 1.5 seconds; reading it more often
  will do no harm, but will return 'old' values.

  To change sensor N to a thermistor, 'echo 4 > tempN_type' where N is 1, 2,

  or 3. To change sensor N to a thermal diode, 'echo 3 > tempN_type'.
  Give 0 for unused sensor. Any other value is invalid. To configure this at

  startup, consult lm_sensors's /etc/sensors.conf. (4 = thermistor;

  3 = thermal diode)

  
  Fan speed control
  -----------------

  The fan speed control features are limited to manual PWM mode. Automatic

  "Smart Guardian" mode control handling is only implemented for older chips
  (see below.) However if you want to go for "manual mode" just write 1 to
  pwmN_enable.

  
  If you are only able to control the fan speed with very small PWM values,
  try lowering the PWM base frequency (pwm1_freq). Depending on the fan,
  it may give you a somewhat greater control range. The same frequency is
  used to drive all fan outputs, which is why pwm2_freq and pwm3_freq are
  read-only.

  
  
  Automatic fan speed control (old interface)
  -------------------------------------------
  
  The driver supports the old interface to automatic fan speed control
  which is implemented by IT8705F chips up to revision F and IT8712F
  chips up to revision G.
  
  This interface implements 4 temperature vs. PWM output trip points.
  The PWM output of trip point 4 is always the maximum value (fan running
  at full speed) while the PWM output of the other 3 trip points can be
  freely chosen. The temperature of all 4 trip points can be freely chosen.
  Additionally, trip point 1 has an hysteresis temperature attached, to
  prevent fast switching between fan on and off.
  
  The chip automatically computes the PWM output value based on the input
  temperature, based on this simple rule: if the temperature value is
  between trip point N and trip point N+1 then the PWM output value is
  the one of trip point N. The automatic control mode is less flexible
  than the manual control mode, but it reacts faster, is more robust and
  doesn't use CPU cycles.

  
  Trip points must be set properly before switching to automatic fan speed
  control mode. The driver will perform basic integrity checks before
  actually switching to automatic control mode.