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diff --git a/Documentation/hwmon/g762.rst b/Documentation/hwmon/g762.rst new file mode 100644 index 0000000000..0371b3365c --- /dev/null +++ b/Documentation/hwmon/g762.rst @@ -0,0 +1,74 @@ +Kernel driver g762 +================== + +The GMT G762 Fan Speed PWM Controller is connected directly to a fan +and performs closed-loop or open-loop control of the fan speed. Two +modes - PWM or DC - are supported by the device. + +For additional information, a detailed datasheet is available at +http://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfs +bindings 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 usually +done via a userland daemon like fancontrol. + +Note that those entries do not provide ways to setup the specific +hardware characteristics of the system (reference clock, pulses per +fan revolution, ...); Those can be modified via devicetree bindings +documented in Documentation/devicetree/bindings/hwmon/g762.txt or +using a specific platform_data structure in board initialization +file (see include/linux/platform_data/g762.h). + + fan1_target: + set desired fan speed. This only makes sense in closed-loop + fan speed control (i.e. when pwm1_enable is set to 2). + + fan1_input: + provide current fan rotation value in RPM as reported by + the 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 values + are 2 and 4. + + fan1_fault: + reports fan failure, i.e. no transition on fan gear pin for + about 0.7s (if the fan is not voluntarily set off). + + fan1_alarm: + in closed-loop control mode, if fan RPM value is 25% out + of the programmed value for over 6 seconds 'fan1_alarm' is + set to 1. + + pwm1_enable: + set current fan speed control mode i.e. 1 for manual fan + speed control (open-loop) via pwm1 described below, 2 for + automatic fan speed control (closed-loop) via fan1_target + above. + + 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 an + integer value between 0 and 255. 0 stops the fan, 255 makes + it 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 to +the chip via 'fan1_target'. In closed-loop mode, the target speed is compared +with current speed (available via 'fan1_input') by the device and a feedback +is performed to match that target value. The fan speed value is computed +based on the parameters associated with the physical characteristics of the +system: a reference clock source frequency, a number of pulses per fan +revolution, etc. + +Note that the driver will update its values at most once per second. |