| xj | b04a402 | 2021-11-25 15:01:52 +0800 | [diff] [blame] | 1 | Kernel driver g762 |
| 2 | ================== |
| 3 | |
| 4 | The GMT G762 Fan Speed PWM Controller is connected directly to a fan |
| 5 | and performs closed-loop or open-loop control of the fan speed. Two |
| 6 | modes - PWM or DC - are supported by the device. |
| 7 | |
| 8 | For additional information, a detailed datasheet is available at |
| 9 | http://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfs |
| 10 | bindings are described in Documentation/hwmon/sysfs-interface. |
| 11 | |
| 12 | The following entries are available to the user in a subdirectory of |
| 13 | /sys/bus/i2c/drivers/g762/ to control the operation of the device. |
| 14 | This can be done manually using the following entries but is usually |
| 15 | done via a userland daemon like fancontrol. |
| 16 | |
| 17 | Note that those entries do not provide ways to setup the specific |
| 18 | hardware characteristics of the system (reference clock, pulses per |
| 19 | fan revolution, ...); Those can be modified via devicetree bindings |
| 20 | documented in Documentation/devicetree/bindings/hwmon/g762.txt or |
| 21 | using a specific platform_data structure in board initialization |
| 22 | file (see include/linux/platform_data/g762.h). |
| 23 | |
| 24 | fan1_target: set desired fan speed. This only makes sense in closed-loop |
| 25 | fan speed control (i.e. when pwm1_enable is set to 2). |
| 26 | |
| 27 | fan1_input: provide current fan rotation value in RPM as reported by |
| 28 | the fan to the device. |
| 29 | |
| 30 | fan1_div: fan clock divisor. Supported value are 1, 2, 4 and 8. |
| 31 | |
| 32 | fan1_pulses: number of pulses per fan revolution. Supported values |
| 33 | are 2 and 4. |
| 34 | |
| 35 | fan1_fault: reports fan failure, i.e. no transition on fan gear pin for |
| 36 | about 0.7s (if the fan is not voluntarily set off). |
| 37 | |
| 38 | fan1_alarm: in closed-loop control mode, if fan RPM value is 25% out |
| 39 | of the programmed value for over 6 seconds 'fan1_alarm' is |
| 40 | set to 1. |
| 41 | |
| 42 | pwm1_enable: set current fan speed control mode i.e. 1 for manual fan |
| 43 | speed control (open-loop) via pwm1 described below, 2 for |
| 44 | automatic fan speed control (closed-loop) via fan1_target |
| 45 | above. |
| 46 | |
| 47 | pwm1_mode: set or get fan driving mode: 1 for PWM mode, 0 for DC mode. |
| 48 | |
| 49 | pwm1: get or set PWM fan control value in open-loop mode. This is an |
| 50 | integer value between 0 and 255. 0 stops the fan, 255 makes |
| 51 | it run at full speed. |
| 52 | |
| 53 | Both in PWM mode ('pwm1_mode' set to 1) and DC mode ('pwm1_mode' set to 0), |
| 54 | when current fan speed control mode is open-loop ('pwm1_enable' set to 1), |
| 55 | the fan speed is programmed by setting a value between 0 and 255 via 'pwm1' |
| 56 | entry (0 stops the fan, 255 makes it run at full speed). In closed-loop mode |
| 57 | ('pwm1_enable' set to 2), the expected rotation speed in RPM can be passed to |
| 58 | the chip via 'fan1_target'. In closed-loop mode, the target speed is compared |
| 59 | with current speed (available via 'fan1_input') by the device and a feedback |
| 60 | is performed to match that target value. The fan speed value is computed |
| 61 | based on the parameters associated with the physical characteristics of the |
| 62 | system: a reference clock source frequency, a number of pulses per fan |
| 63 | revolution, etc. |
| 64 | |
| 65 | Note that the driver will update its values at most once per second. |