hwmon: (nct6775) Add support for temperature sensors

[mirror_ubuntu-artful-kernel.git] / Documentation / hwmon / nct6775

Note
====

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

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

Supported chips:
  * Nuvoton NCT6775F/W83667HG-I
    Prefix: 'nct6775'
    Addresses scanned: ISA address retrieved from Super I/O registers
    Datasheet: Available from Nuvoton upon request
  * Nuvoton NCT6776F
    Prefix: 'nct6776'
    Addresses scanned: ISA address retrieved from Super I/O registers
    Datasheet: Available from Nuvoton upon request
  * Nuvoton NCT6779D
    Prefix: 'nct6779'
    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
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 doubles the divider value each time a fan speed reading
returns an invalid value. 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.

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