Kernel driver g762

The GMT G762 Fan Speed PWM Controller is connected directly to a fanand performs closed-loop or open-loop control of the fan speed. Twomodes - PWM or DC - are supported by the device.

For additional information, a detailed datasheet is available athttp://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfsbindings are described in Documentation/hwmon/sysfs-interface.rst.

The following entries are available to the user in a subdirectory of/sys/bus/i2c/drivers/g762/ to control the operation of the device.This can be done manually using the following entries but is usuallydone via a userland daemon like fancontrol.

Note that those entries do not provide ways to setup the specifichardware characteristics of the system (reference clock, pulses perfan revolution, …); Those can be modified via devicetree bindingsdocumented in Documentation/devicetree/bindings/hwmon/g762.txt orusing a specific platform_data structure in board initializationfile (see include/linux/platform_data/g762.h).

fan1_target:
set desired fan speed. This only makes sense in closed-loopfan speed control (i.e. when pwm1_enable is set to 2).
fan1_input:
provide current fan rotation value in RPM as reported bythe fan to the device.
fan1_div:
fan clock divisor. Supported value are 1, 2, 4 and 8.
fan1_pulses:
number of pulses per fan revolution. Supported valuesare 2 and 4.
fan1_fault:
reports fan failure, i.e. no transition on fan gear pin forabout 0.7s (if the fan is not voluntarily set off).
fan1_alarm:
in closed-loop control mode, if fan RPM value is 25% outof the programmed value for over 6 seconds ‘fan1_alarm’ isset to 1.
pwm1_enable:
set current fan speed control mode i.e. 1 for manual fanspeed control (open-loop) via pwm1 described below, 2 forautomatic fan speed control (closed-loop) via fan1_targetabove.
pwm1_mode:
set or get fan driving mode: 1 for PWM mode, 0 for DC mode.
pwm1:
get or set PWM fan control value in open-loop mode. This is aninteger value between 0 and 255. 0 stops the fan, 255 makesit run at full speed.

Both in PWM mode (‘pwm1_mode’ set to 1) and DC mode (‘pwm1_mode’ set to 0),when current fan speed control mode is open-loop (‘pwm1_enable’ set to 1),the fan speed is programmed by setting a value between 0 and 255 via ‘pwm1’entry (0 stops the fan, 255 makes it run at full speed). In closed-loop mode(‘pwm1_enable’ set to 2), the expected rotation speed in RPM can be passed tothe chip via ‘fan1_target’. In closed-loop mode, the target speed is comparedwith current speed (available via ‘fan1_input’) by the device and a feedbackis performed to match that target value. The fan speed value is computedbased on the parameters associated with the physical characteristics of thesystem: a reference clock source frequency, a number of pulses per fanrevolution, etc.

Note that the driver will update its values at most once per second.