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Arnaud Ebalard594fbe72013-06-20 22:21:04 +02001Kernel 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.
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: 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
53Both in PWM mode ('pwm1_mode' set to 1) and DC mode ('pwm1_mode' set to 0),
54when current fan speed control mode is open-loop ('pwm1_enable' set to 1),
55the fan speed is programmed by setting a value between 0 and 255 via 'pwm1'
56entry (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
58the chip via 'fan1_target'. In closed-loop mode, the target speed is compared
59with current speed (available via 'fan1_input') by the device and a feedback
60is performed to match that target value. The fan speed value is computed
61based on the parameters associated with the physical characteristics of the
62system: a reference clock source frequency, a number of pulses per fan
63revolution, etc.
64
65Note that the driver will update its values at most once per second.