75 lines
3.0 KiB
ReStructuredText
75 lines
3.0 KiB
ReStructuredText
Kernel driver g762
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==================
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The GMT G762 Fan Speed PWM Controller is connected directly to a fan
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and performs closed-loop or open-loop control of the fan speed. Two
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modes - PWM or DC - are supported by the device.
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For additional information, a detailed datasheet is available at
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http://natisbad.org/NAS/ref/GMT_EDS-762_763-080710-0.2.pdf. sysfs
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bindings are described in Documentation/hwmon/sysfs-interface.rst.
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The following entries are available to the user in a subdirectory of
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/sys/bus/i2c/drivers/g762/ to control the operation of the device.
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This can be done manually using the following entries but is usually
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done via a userland daemon like fancontrol.
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Note that those entries do not provide ways to setup the specific
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hardware characteristics of the system (reference clock, pulses per
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fan revolution, ...); Those can be modified via devicetree bindings
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documented in Documentation/devicetree/bindings/hwmon/g762.txt or
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using a specific platform_data structure in board initialization
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file (see include/linux/platform_data/g762.h).
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fan1_target:
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set desired fan speed. This only makes sense in closed-loop
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fan speed control (i.e. when pwm1_enable is set to 2).
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fan1_input:
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provide current fan rotation value in RPM as reported by
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the fan to the device.
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fan1_div:
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fan clock divisor. Supported value are 1, 2, 4 and 8.
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fan1_pulses:
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number of pulses per fan revolution. Supported values
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are 2 and 4.
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fan1_fault:
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reports fan failure, i.e. no transition on fan gear pin for
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about 0.7s (if the fan is not voluntarily set off).
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fan1_alarm:
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in closed-loop control mode, if fan RPM value is 25% out
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of the programmed value for over 6 seconds 'fan1_alarm' is
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set to 1.
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pwm1_enable:
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set current fan speed control mode i.e. 1 for manual fan
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speed control (open-loop) via pwm1 described below, 2 for
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automatic fan speed control (closed-loop) via fan1_target
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above.
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pwm1_mode:
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set or get fan driving mode: 1 for PWM mode, 0 for DC mode.
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pwm1:
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get or set PWM fan control value in open-loop mode. This is an
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integer value between 0 and 255. 0 stops the fan, 255 makes
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it run at full speed.
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Both in PWM mode ('pwm1_mode' set to 1) and DC mode ('pwm1_mode' set to 0),
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when current fan speed control mode is open-loop ('pwm1_enable' set to 1),
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the fan speed is programmed by setting a value between 0 and 255 via 'pwm1'
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entry (0 stops the fan, 255 makes it run at full speed). In closed-loop mode
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('pwm1_enable' set to 2), the expected rotation speed in RPM can be passed to
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the chip via 'fan1_target'. In closed-loop mode, the target speed is compared
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with current speed (available via 'fan1_input') by the device and a feedback
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is performed to match that target value. The fan speed value is computed
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based on the parameters associated with the physical characteristics of the
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system: a reference clock source frequency, a number of pulses per fan
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revolution, etc.
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Note that the driver will update its values at most once per second.
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