hwmon: Documentation update for w83627ehf

Kernel driver w83627ehf

=======================

Supported chips:

  * Winbond W83627EHF/EHG (ISA access ONLY)

    Prefix: 'w83627ehf'

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

    Datasheet: http://www.winbond-usa.com/products/winbond_products/pdfs/PCIC/W83627EHF_%20W83627EHGb.pdf

Authors:

        Jean Delvare <khali@linux-fr.org>

        Yuan Mu <Ymu@Winbond.com.tw>

        Rudolf Marek <r.marek@sh.cvut.cz>

Description

-----------

This driver implements support for the Winbond W83627EHF and W83627EHG

super I/O chips. We will refer to them collectively as Winbond chips.

The chips implement three temperature sensors, five fan rotation

speed sensors, ten analog voltage sensors, alarms with beep warnings (control

unimplemented), and some automatic fan regulation strategies (plus manual

fan control mode).

Temperatures are measured in degrees Celsius and measurement resolution is 1

degC for temp1 and 0.5 degC for temp2 and temp3. An alarm is triggered when

the temperature gets higher than high limit; it stays on until the temperature

falls below the Hysteresis value.

Fan rotation speeds are reported in RPM (rotations per minute). An alarm is

triggered if the rotation speed has dropped below a programmable limit. 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 driver sets the most

suitable fan divisor itself. 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-fan4. Mapping of temperatures to pwm outputs is as

follows:

temp1 -> pwm1

temp2 -> pwm2

temp3 -> pwm3

prog  -> pwm4 (the programmable setting is not supported by the driver)

/sys files

----------

pwm[1-4] - this file stores PWM duty cycle or DC value (fan speed) in range:

	   0 (stop) to 255 (full)

pwm[1-4]_enable - this file controls mode of fan/temperature control:

	* 1 Manual Mode, write to pwm file any value 0-255 (full speed)

	* 2 Thermal Cruise

Thermal Cruise mode

-------------------

If the temperature is in the range defined by:

pwm[1-4]_target    - set target temperature, unit millidegree Celcius

		     (range 0 - 127000)

pwm[1-4]_tolerance - tolerance, unit millidegree Celcius (range 0 - 15000)

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

fan speed increases (temp is higher) or decreases if lower than desired.

There are defined steps and times, but not exported by the driver yet.

pwm[1-4]_min_output - minimum fan speed (range 1 - 255), when the temperature

                      is below defined range.

pwm[1-4]_stop_time  - how many milliseconds [ms] must elapse to switch

                      corresponding fan off. (when the temperature was below

                      defined range).

Note: last two functions are influenced by other control bits, not yet exported

      by the driver, so a change might not have any effect.