1Kernel driver g762 2================== 3 4The GMT G762 Fan Speed PWM Controller is connected directly to a fan 5and performs closed-loop or open-loop control of the fan speed. Two 6modes - PWM or DC - are supported by the device. 7 8For additional information, a detailed datasheet is available at 9http://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfs 10bindings are described in Documentation/hwmon/sysfs-interface.rst. 11 12The following entries are available to the user in a subdirectory of 13/sys/bus/i2c/drivers/g762/ to control the operation of the device. 14This can be done manually using the following entries but is usually 15done via a userland daemon like fancontrol. 16 17Note that those entries do not provide ways to setup the specific 18hardware characteristics of the system (reference clock, pulses per 19fan revolution, ...); Those can be modified via devicetree bindings 20documented in Documentation/devicetree/bindings/hwmon/g762.txt or 21using a specific platform_data structure in board initialization 22file (see include/linux/platform_data/g762.h). 23 24 fan1_target: 25 set desired fan speed. This only makes sense in closed-loop 26 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 by 30 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 values 37 are 2 and 4. 38 39 fan1_fault: 40 reports fan failure, i.e. no transition on fan gear pin for 41 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% out 45 of the programmed value for over 6 seconds 'fan1_alarm' is 46 set to 1. 47 48 pwm1_enable: 49 set current fan speed control mode i.e. 1 for manual fan 50 speed control (open-loop) via pwm1 described below, 2 for 51 automatic fan speed control (closed-loop) via fan1_target 52 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 an 59 integer value between 0 and 255. 0 stops the fan, 255 makes 60 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 mode 66('pwm1_enable' set to 2), the expected rotation speed in RPM can be passed to 67the chip via 'fan1_target'. In closed-loop mode, the target speed is compared 68with current speed (available via 'fan1_input') by the device and a feedback 69is performed to match that target value. The fan speed value is computed 70based on the parameters associated with the physical characteristics of the 71system: a reference clock source frequency, a number of pulses per fan 72revolution, etc. 73 74Note that the driver will update its values at most once per second. 75