LXR linux/Documentation/hwmon/g762.rst

   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