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1Kernel driver g7622==================3 4The GMT G762 Fan Speed PWM Controller is connected directly to a fan5and performs closed-loop or open-loop control of the fan speed. Two6modes - PWM or DC - are supported by the device.7 8For additional information, a detailed datasheet is available at9http://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfs10bindings are described in Documentation/hwmon/sysfs-interface.rst.11 12The following entries are available to the user in a subdirectory of13/sys/bus/i2c/drivers/g762/ to control the operation of the device.14This can be done manually using the following entries but is usually15done via a userland daemon like fancontrol.16 17Note that those entries do not provide ways to setup the specific18hardware characteristics of the system (reference clock, pulses per19fan revolution, ...); Those can be modified via devicetree bindings20documented in Documentation/devicetree/bindings/hwmon/g762.txt or21using a specific platform_data structure in board initialization22file (see include/linux/platform_data/g762.h).23 24 fan1_target:25 set desired fan speed. This only makes sense in closed-loop26 fan speed control (i.e. when pwm1_enable is set to 2).27 28 fan1_input:29 provide current fan rotation value in RPM as reported by30 the fan to the device.31 32 fan1_div:33 fan clock divisor. Supported value are 1, 2, 4 and 8.34 35 fan1_pulses:36 number of pulses per fan revolution. Supported values37 are 2 and 4.38 39 fan1_fault:40 reports fan failure, i.e. no transition on fan gear pin for41 about 0.7s (if the fan is not voluntarily set off).42 43 fan1_alarm:44 in closed-loop control mode, if fan RPM value is 25% out45 of the programmed value for over 6 seconds 'fan1_alarm' is46 set to 1.47 48 pwm1_enable:49 set current fan speed control mode i.e. 1 for manual fan50 speed control (open-loop) via pwm1 described below, 2 for51 automatic fan speed control (closed-loop) via fan1_target52 above.53 54 pwm1_mode:55 set or get fan driving mode: 1 for PWM mode, 0 for DC mode.56 57 pwm1:58 get or set PWM fan control value in open-loop mode. This is an59 integer value between 0 and 255. 0 stops the fan, 255 makes60 it run at full speed.61 62Both in PWM mode ('pwm1_mode' set to 1) and DC mode ('pwm1_mode' set to 0),63when current fan speed control mode is open-loop ('pwm1_enable' set to 1),64the fan speed is programmed by setting a value between 0 and 255 via 'pwm1'65entry (0 stops the fan, 255 makes it run at full speed). In closed-loop mode66('pwm1_enable' set to 2), the expected rotation speed in RPM can be passed to67the chip via 'fan1_target'. In closed-loop mode, the target speed is compared68with current speed (available via 'fan1_input') by the device and a feedback69is performed to match that target value. The fan speed value is computed70based on the parameters associated with the physical characteristics of the71system: a reference clock source frequency, a number of pulses per fan72revolution, etc.73 74Note that the driver will update its values at most once per second.75