1*4882a593SmuzhiyunKernel driver g762 2*4882a593Smuzhiyun================== 3*4882a593Smuzhiyun 4*4882a593SmuzhiyunThe GMT G762 Fan Speed PWM Controller is connected directly to a fan 5*4882a593Smuzhiyunand performs closed-loop or open-loop control of the fan speed. Two 6*4882a593Smuzhiyunmodes - PWM or DC - are supported by the device. 7*4882a593Smuzhiyun 8*4882a593SmuzhiyunFor additional information, a detailed datasheet is available at 9*4882a593Smuzhiyunhttp://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfs 10*4882a593Smuzhiyunbindings are described in Documentation/hwmon/sysfs-interface.rst. 11*4882a593Smuzhiyun 12*4882a593SmuzhiyunThe following entries are available to the user in a subdirectory of 13*4882a593Smuzhiyun/sys/bus/i2c/drivers/g762/ to control the operation of the device. 14*4882a593SmuzhiyunThis can be done manually using the following entries but is usually 15*4882a593Smuzhiyundone via a userland daemon like fancontrol. 16*4882a593Smuzhiyun 17*4882a593SmuzhiyunNote that those entries do not provide ways to setup the specific 18*4882a593Smuzhiyunhardware characteristics of the system (reference clock, pulses per 19*4882a593Smuzhiyunfan revolution, ...); Those can be modified via devicetree bindings 20*4882a593Smuzhiyundocumented in Documentation/devicetree/bindings/hwmon/g762.txt or 21*4882a593Smuzhiyunusing a specific platform_data structure in board initialization 22*4882a593Smuzhiyunfile (see include/linux/platform_data/g762.h). 23*4882a593Smuzhiyun 24*4882a593Smuzhiyun fan1_target: 25*4882a593Smuzhiyun set desired fan speed. This only makes sense in closed-loop 26*4882a593Smuzhiyun fan speed control (i.e. when pwm1_enable is set to 2). 27*4882a593Smuzhiyun 28*4882a593Smuzhiyun fan1_input: 29*4882a593Smuzhiyun provide current fan rotation value in RPM as reported by 30*4882a593Smuzhiyun the fan to the device. 31*4882a593Smuzhiyun 32*4882a593Smuzhiyun fan1_div: 33*4882a593Smuzhiyun fan clock divisor. Supported value are 1, 2, 4 and 8. 34*4882a593Smuzhiyun 35*4882a593Smuzhiyun fan1_pulses: 36*4882a593Smuzhiyun number of pulses per fan revolution. Supported values 37*4882a593Smuzhiyun are 2 and 4. 38*4882a593Smuzhiyun 39*4882a593Smuzhiyun fan1_fault: 40*4882a593Smuzhiyun reports fan failure, i.e. no transition on fan gear pin for 41*4882a593Smuzhiyun about 0.7s (if the fan is not voluntarily set off). 42*4882a593Smuzhiyun 43*4882a593Smuzhiyun fan1_alarm: 44*4882a593Smuzhiyun in closed-loop control mode, if fan RPM value is 25% out 45*4882a593Smuzhiyun of the programmed value for over 6 seconds 'fan1_alarm' is 46*4882a593Smuzhiyun set to 1. 47*4882a593Smuzhiyun 48*4882a593Smuzhiyun pwm1_enable: 49*4882a593Smuzhiyun set current fan speed control mode i.e. 1 for manual fan 50*4882a593Smuzhiyun speed control (open-loop) via pwm1 described below, 2 for 51*4882a593Smuzhiyun automatic fan speed control (closed-loop) via fan1_target 52*4882a593Smuzhiyun above. 53*4882a593Smuzhiyun 54*4882a593Smuzhiyun pwm1_mode: 55*4882a593Smuzhiyun set or get fan driving mode: 1 for PWM mode, 0 for DC mode. 56*4882a593Smuzhiyun 57*4882a593Smuzhiyun pwm1: 58*4882a593Smuzhiyun get or set PWM fan control value in open-loop mode. This is an 59*4882a593Smuzhiyun integer value between 0 and 255. 0 stops the fan, 255 makes 60*4882a593Smuzhiyun it run at full speed. 61*4882a593Smuzhiyun 62*4882a593SmuzhiyunBoth in PWM mode ('pwm1_mode' set to 1) and DC mode ('pwm1_mode' set to 0), 63*4882a593Smuzhiyunwhen current fan speed control mode is open-loop ('pwm1_enable' set to 1), 64*4882a593Smuzhiyunthe fan speed is programmed by setting a value between 0 and 255 via 'pwm1' 65*4882a593Smuzhiyunentry (0 stops the fan, 255 makes it run at full speed). In closed-loop mode 66*4882a593Smuzhiyun('pwm1_enable' set to 2), the expected rotation speed in RPM can be passed to 67*4882a593Smuzhiyunthe chip via 'fan1_target'. In closed-loop mode, the target speed is compared 68*4882a593Smuzhiyunwith current speed (available via 'fan1_input') by the device and a feedback 69*4882a593Smuzhiyunis performed to match that target value. The fan speed value is computed 70*4882a593Smuzhiyunbased on the parameters associated with the physical characteristics of the 71*4882a593Smuzhiyunsystem: a reference clock source frequency, a number of pulses per fan 72*4882a593Smuzhiyunrevolution, etc. 73*4882a593Smuzhiyun 74*4882a593SmuzhiyunNote that the driver will update its values at most once per second. 75