Merge branch 'pwm_fan_page' into wiki_update
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Aditya Prayoga
commit
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361
docs/pwm.md
361
docs/pwm.md
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@ -1,2 +1,361 @@
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!!! warning
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Always POWER OFF the system before plug/unplug the fan. Failed to do so could damage the controlling GPIO due to power surge.
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## PWM Introduction
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PWM, or pulse width modulation is a technique which allows us to adjust the average value of the voltage that’s going to the electronic device by varying duty cycle of the power at a fast rate.
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The term *duty cycle* describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. When a digital signal is on half of the time and off the other half of the time, the digital signal has a duty cycle of 50% and resembles a "square" wave. When a digital signal spends more time in the on state than the off state, it has a duty cycle of >50%. When a digital signal spends more time in the off state than the on state, it has a duty cycle of <50%. Here is a pictorial that illustrates these three scenarios:
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## PWM Fan Implementation
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### Type A
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### Type B
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### Type C
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## Helios4 Fan Control Schematic
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| Description | Connector J10 | J17 | Remarks |
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|-----------|---------|-----------|---------|
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| PWM pin | gpio41 | gpio55 | 3.3V pull up fan **ONLY**! Early generation of 4-wire pwm fan may use 5V pull-up |
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| SENSE pin | gpio43 | gpio48 | SENSE pin is not used yet |
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| PWM Frequency | 25 kHz | 25 kHz | defined in device tree |
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## Bundled Fan
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Connector Pinout
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| Pin | Function | Wire Color |
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|-----|----------|------------|
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| 1 | GND | Black |
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| 2 | 12V | Red |
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| 3 | Sense | Yellow |
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| 4 | Control | Blue |
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### Old Fan (Batch 1)
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Fan Specification
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| Parameter | Value | Unit | Remarks |
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|---------------|----------|------|---------|
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| Maximum Speed | 4200 | RPM | @ duty cycle 98% |
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| Minimum Speed | 1200 | RPM | @ duty cycle 24% |
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| Shut off | No | | Not Supported |
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| Implementation Type | A | | |
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!!! info
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Coming soon.
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Duty cycle data is converted from Linux PWM
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### New Fan (Batch 2)
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Fan Specification
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| Parameter | Value | Unit | Remarks |
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|---------------|----------|------|---------|
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| Maximum Speed | 4200 | RPM | @ duty cycle 98% |
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| Minimum Speed | 400 | RPM | @ duty cycle 10% |
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| Shut off | Yes | | duty cycle <= 5.5% and restart @ duty cycle > 9% |
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| Implementation Type | C | | |
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!!! info
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Duty cycle data is converted from Linux PWM
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### Fan Speed Comparison
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## Helios4 Temperature Sensors
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### CPU Thermal Sensor
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Armada 388 incorporates a Thermal Management engine for monitoring die temperature. It includes an on-die analog-to-digital thermal sensor, that is used to determine when the maximum specified processor junction temperature has been reached.
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### Ethernet PHY Thermal Sensor
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Helios4's **10/100/1000 BASE-T PHY Tranceiver** ([Marvell 88E1512 Datasheet](http://www.marvell.com/documents/eoxwrbluvwybgxvagkkf/)) features an internal temperature sensor. The sensor reports the die temperature and is updated approximately once per second.
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### Board Temp Sensor
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Helios4 has a **Digital Temperature Sensor with 2‐wire Interface** ([NCT75 Datasheet](https://www.onsemi.com/pub/Collateral/NCT75-D.PDF)), located on bottom side of the board. It is used to read ambient temperature.
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## PWM Fan Control under Linux
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Linux use 8-bit integer to represent duty cycle. PWM value 0 represent 0% duty cycle and PWM value 255 represent 100% duty cycle.
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Below graphs are bundled fan speed vs pwm value instead of duty cycle.
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Currently Linux gpio-mvebu driver does not allow more than 1 PWM under the same bank. Helios4 uses 2 PWM under same bank therefore [this patch](https://raw.githubusercontent.com/armbian/build/master/patch/kernel/mvebu-next/92-mvebu-gpio-remove-hardcoded-timer-assignment.patch) needs to be applied to kernel source to remove the restriction.
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### Using SYSFS interface
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Linux export the fan control mechanism to SYSFS under hwmon class.
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List of devices can be checked under /sys/class/hwmon
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```
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ls -l /sys/class/hwmon/
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total 0
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lrwxrwxrwx 1 root root 0 Nov 7 07:23 hwmon0 -> ../../devices/platform/soc/soc:internal-regs/f1072004.mdio/mdio_bus/f1072004.mdio-mii/f1072004.mdio-mii:00/hwmon/hwmon0
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lrwxrwxrwx 1 root root 0 Nov 7 07:23 hwmon1 -> ../../devices/virtual/hwmon/hwmon1
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lrwxrwxrwx 1 root root 0 Nov 7 07:23 hwmon2 -> ../../devices/platform/j10-pwm/hwmon/hwmon2
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lrwxrwxrwx 1 root root 0 Nov 7 07:23 hwmon3 -> ../../devices/platform/j17-pwm/hwmon/hwmon3
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lrwxrwxrwx 1 root root 0 Nov 7 07:23 hwmon4 -> ../../devices/platform/soc/soc:internal-regs/f1011000.i2c/i2c-0/0-004c/hwmon/hwmon4
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```
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!!! info
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The numbering may different from above example output. It depends on whether the driver built as kernel module or built-in, device initialization order. Take this as consideration when using [fancontrol](#fancontrol-automated-software-based-fan-speed-regulation)
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To identify which hwmon belong to fan, look for *j10-pwm* and *j17-pwm*. On above example
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```
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hwmon2 -> ../../devices/platform/j10-pwm/hwmon/hwmon2
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hwmon3 -> ../../devices/platform/j17-pwm/hwmon/hwmon3
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```
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To read current PWM
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```
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cat /sys/class/hwmon2/pwm1
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cat /sys/class/hwmon3/pwm1
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```
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To set PWM
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```
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echo NEW_PWM_VALUE > /sys/class/hwmon2/pwm1
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echo NEW_PWM_VALUE > /sys/class/hwmon3/pwm1
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```
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### Fancontrol - automated software based fan speed regulation
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fancontrol is a shell script for use with lm_sensors. It reads its configuration from a file, then calculates fan speeds from temperatures and sets the corresponding PWM outputs to the computed values.
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fancontrol include *pwmconfig* script to create a configuration file but it can not be used in Helios4.
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#### Configuration File
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fancontrol uses **/etc/fancontrol** as configuration file. Below is an example configuration to control fan speed on Helios4.
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```
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# Helios4 PWM Fan Control Configuration
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# Temp source : armada_thermal sensor
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INTERVAL=10
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DEVPATH=hwmon2=devices/platform/j10-pwm hwmon3=devices/platform/j17-pwm hwmon4=devices/platform/soc/soc:internal-regs/f1011000.i2c/i2c-0/0-004c
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DEVNAME=hwmon1=armada_thermal
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FCTEMPS=hwmon2/pwm1=hwmon1/temp1_input hwmon3/pwm1=hwmon1/temp1_input
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MINTEMP=hwmon2/pwm1=70 hwmon3/pwm1=70
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MAXTEMP=hwmon2/pwm1=90 hwmon3/pwm1=90
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MINSTART=hwmon2/pwm1=20 hwmon3/pwm1=20
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MINSTOP=hwmon2/pwm1=29 hwmon3/pwm1=29
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MINPWM=0
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```
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INTERVAL
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This variable defines at which interval in seconds the main loop of fancontrol will be executed
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DEVPATH
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Maps hwmon class devices to physical devices. This lets fancontrol check that the configuration file is still up-to-date.
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It expect the **hwmonN** as symlink to **devices/***
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DEVNAME
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Records hwmon class device names. This lets fancontrol check that the configuration file is still up-to-date.
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Since **armada_thermal** does not create symlink, use *DEVNAME* instead of *DEVPATH*
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FCTEMPS
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Maps PWM outputs to temperature sensors so fancontrol knows which temperature sensors should be used for calculation of new values for the corresponding PWM outputs.
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Fans (**hwmon2** & **hwmon3**) are controlled based on CPU thermal sensor (**hwmon1**) reading.
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MINSTART
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Sets the minimum speed at which the fan begins spinning. You should use a safe value to be sure it works, even when the fan gets old.
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New bundled fan restart at 15, added 5 for safety (in case of aging fan) give us **20**. The value does not affect old bundle fan.
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MINSTOP
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The minimum speed at which the fan still spins. Use a safe value here, too.
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New bundled fan stopped at 24, added 5 for safety (in case of aging fan) give us **29**. The value does not affect old bundle fan.
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-----
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*Following settings can be adjusted by user to tweak further.*
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MINTEMP
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The temperature below which the fan gets switched to minimum speed.
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Fans (hwmon2 & hwmon3) runs in minimum speed if the CPU temperature below **70** degree C.
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MAXTEMP
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The temperature over which the fan gets switched to maximum speed.
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Fans (hwmon2 & hwmon3) runs in maximum speed if the CPU temperature above **90** degree C.
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MINPWM
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The PWM value to use when the temperature is below MINTEMP. Typically, this will be either 0 if it is OK for the fan to plain stop, or the same value as MINSTOP if you don't want the fan to ever stop. If this value isn't defined, it defaults to 0 (stopped fan).
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Set minimum PWM value to **0**. On new bundled fan, it would stopped the fan while on old bundled fan it would run in minimal speed.
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!!! note
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Since hwmon order can be changed between kernel version or even between reboot, on Armbian we use udev rules as workaround. The rules can be found from [here](https://raw.githubusercontent.com/armbian/build/master/packages/bsp/helios4/90-helios4-hwmon.rules) and the configuration file can be found [here](https://raw.githubusercontent.com/armbian/build/master/packages/bsp/helios4/fancontrol_pwm-fan-mvebu-next.conf)
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### Thermal Zone on Device Tree
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Linux provide Thermal Framework to do thermal management. By using this method to control the fan speed, no userspace such as [fancontrol](#fancontrol-automated-software-based-fan-speed-regulation) is required.
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Below are device tree nodes that can be added to Helios4 device tree to make use of Linux Thermal Framework.
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```
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/ {
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...
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fan1: j10-pwm {
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compatible = "pwm-fan";
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pwms = <&gpio1 9 40000>; /* Target freq:25 kHz */
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cooling-min-state = <0>;
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cooling-max-state = <3>;
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#cooling-cells = <2>;
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cooling-levels = <0 25 128 255>;
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};
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fan2: j17-pwm {
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compatible = "pwm-fan";
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pwms = <&gpio1 23 40000>; /* Target freq:25 kHz */
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cooling-min-state = <0>;
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cooling-max-state = <3>;
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#cooling-cells = <2>;
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cooling-levels = <0 25 128 255>;
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};
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thermal-zones {
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microsom_thermal: microsom-thermal {
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thermal-sensors = <&thermal>;
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polling-delay-passive = <250>; /* milliseconds */
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polling-delay = <500>; /* milliseconds */
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trips {
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cpu_active: cpu_active {
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/* millicelsius */
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temperature = <70000>;
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hysteresis = <2000>;
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type = "active";
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};
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cpu_alert: cpu_alert {
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/* millicelsius */
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temperature = <90000>;
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hysteresis = <2000>;
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type = "hot";
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};
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cpu_crit: cpu-crit {
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/* millicelsius */
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temperature = <115000>;
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hysteresis = <5000>;
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type = "critical";
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};
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};
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};
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board_thermal: board-thermal {
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thermal-sensors = <&temp_sensor>;
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polling-delay-passive = <0>; /* milliseconds */
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polling-delay = <1500>; /* milliseconds */
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trips {
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board_active: board-active {
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/* millicelsius */
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temperature = <40000>;
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hysteresis = <2000>;
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type = "active";
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};
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board_alert: board-alert {
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/* millicelsius */
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temperature = <60000>;
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hysteresis = <2000>;
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type = "hot";
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};
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board_critical: board-critical {
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/* millicelsius */
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temperature = <70000>;
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hysteresis = <2000>;
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type = "critical";
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};
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};
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cooling-maps {
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map0 {
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trip = <&board_active>;
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cooling-device = <&fan1 THERMAL_NO_LIMIT 2>,
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<&fan2 THERMAL_NO_LIMIT 2>;
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};
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map1 {
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trip = <&board_alert>;
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cooling-device = <&fan1 2 THERMAL_NO_LIMIT>,
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<&fan2 2 THERMAL_NO_LIMIT>;
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};
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};
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};
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};
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...
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};
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&temp_sensor {
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#thermal-sensor-cells = <0>;
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};
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```
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!!! info
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Currently *armada_thermal* driver ([CPU Thermal Sensor](#cpu-thermal-sensor)) does not support thermal-zone binding in device tree, therefore it can not be used as thermal-sensor.
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## References
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[Pulse-width modulation](https://en.wikipedia.org/wiki/Pulse-width_modulation)
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[4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification rev. 1.3](/files/fan/4_Wire_PWM_Spec.pdf)
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[fancontrol man page](https://linux.die.net/man/8/fancontrol)
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[Linux Thermal Framework Device Tree descriptor](https://www.kernel.org/doc/Documentation/devicetree/bindings/thermal/thermal.txt)
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