Hi,
I have a Rock 4 SE from Radxa and I’d like to control a fan. I want it to turn on when the temperature reaches a certain threshold, for example, between 50°C and 60°C. etc.
I’ve connected the fan to the following pins:
Is this wiring correct?
Is there any way or script available to control the fan based on temperature?
what overlay is needed on other OS?
Hi, do you find a solution? If not, I have just developed a script to manage the fan speed based on the CPU temperature. Remember to enable the PWM pin in your SO.
You can find the project on GitHub (I’m not able to post the direct link): albertopiva/linux-fan-manager
Hi! I recently found this post and tried your script on LibreELEC but I could not make use of it and whatever I tried to do I got issues with the device or resource being busy. I decided to post on the LibreELEC-forum and got a response that the script seemed to be built for an older kernel than what they use, do you think it could be possible to see if maybe it is possible to mod your script to also work with LibreELEC?
Thanks for the good work! It looks nice and I hope I can make use of it 
Hello, I have never worked with LibreELEC, the first thing to check is how it manages the PWM. Do you find something about that?
I have absolutely no idea about that, but what I’ve managed to find so far is that LibreELEC is using kernel 6.6 and has libgpiod v2.2 present. I managed to control my PWM fan by hooking up the 5V wire (red) to pin 2, ground (black) to pin 6 and pwm-wire (blue) to pin 11 (GPIO4_C2). Then I can turn the fan on and off by performing gpioset -c 4 18=0 and gpioset -c 4 18=1. I have tried a small bash script in which I simulate some sort of pulse which seem to be working:
for i in $(seq 1 500 ); do gpioset -p 10ms -t0 -c 4 18=1; gpioset -p 10ms -t0 -c 4 18=0; done
Below is a list of the pwm-folders on the system, as noticed there is no “pwm0”-folder present and when trying to enable it (echo 0 > /sys/class/pwm/pwmchip0/export) you are faced with a Device or resource busy error (maybe because it probably should be pwmchip4 and not pwmchip0, but no other chip is present in the folder).
Below you can see the folder structures (also posted on the LibreELEC-forum):
# find /sys -name pwm*
/sys/kernel/debug/pwm
/sys/class/pwm
/sys/class/pwm/pwmchip0
/sys/devices/platform/ff420020.pwm/pwm
/sys/devices/platform/ff420020.pwm/pwm/pwmchip0
/sys/bus/platform/drivers/pwm-clock
/sys/bus/platform/drivers/pwm-regulator
/sys/bus/platform/drivers/pwm-backlight
/sys/firmware/devicetree/base/pwm@ff420020
/sys/firmware/devicetree/base/pwm@ff420010
/sys/firmware/devicetree/base/pwm@ff420000
/sys/firmware/devicetree/base/pinctrl/pwm1
/sys/firmware/devicetree/base/pinctrl/pwm1/pwm1-pin
/sys/firmware/devicetree/base/pinctrl/pwm1/pwm1-pin-pull-down
/sys/firmware/devicetree/base/pinctrl/pwm3a
/sys/firmware/devicetree/base/pinctrl/pwm3a/pwm3a-pin
/sys/firmware/devicetree/base/pinctrl/pwm2
/sys/firmware/devicetree/base/pinctrl/pwm2/pwm2-pin
/sys/firmware/devicetree/base/pinctrl/pwm2/pwm2-pin-pull-down
/sys/firmware/devicetree/base/pinctrl/pwm0
/sys/firmware/devicetree/base/pinctrl/pwm0/pwm0-pin-pull-down
/sys/firmware/devicetree/base/pinctrl/pwm0/pwm0-pin
/sys/firmware/devicetree/base/pinctrl/pwm3b
/sys/firmware/devicetree/base/pinctrl/pwm3b/pwm3b-pin
/sys/firmware/devicetree/base/vdd-log/pwms
/sys/firmware/devicetree/base/vdd-log/pwm-supply
/sys/firmware/devicetree/base/__symbols__/pwm3a_pin
/sys/firmware/devicetree/base/__symbols__/pwm0_pin
/sys/firmware/devicetree/base/__symbols__/pwm3
/sys/firmware/devicetree/base/__symbols__/pwm3b_pin
/sys/firmware/devicetree/base/__symbols__/pwm1
/sys/firmware/devicetree/base/__symbols__/pwm1_pin
/sys/firmware/devicetree/base/__symbols__/pwm1_pin_pull_down
/sys/firmware/devicetree/base/__symbols__/pwm2_pin
/sys/firmware/devicetree/base/__symbols__/pwm2
/sys/firmware/devicetree/base/__symbols__/pwm2_pin_pull_down
/sys/firmware/devicetree/base/__symbols__/pwm0
/sys/firmware/devicetree/base/__symbols__/pwm0_pin_pull_down
/sys/firmware/devicetree/base/pwm@ff420030
# ls -lRt /sys/devices/platform/ff420020.pwm/
/sys/devices/platform/ff420020.pwm/:
total 0
lrwxrwxrwx 1 root root 0 Mar 25 08:29 consumer:platform:vdd-log -> ../../virtual/devlink/platform:ff420020.pwm--platform:vdd-log
lrwxrwxrwx 1 root root 0 Mar 25 08:29 driver -> ../../../bus/platform/drivers/rockchip-pwm
-rw-r--r-- 1 root root 4096 Mar 25 08:29 driver_override
-r--r--r-- 1 root root 4096 Mar 25 08:29 modalias
lrwxrwxrwx 1 root root 0 Mar 25 08:29 of_node -> ../../../firmware/devicetree/base/pwm@ff420020
drwxr-xr-x 2 root root 0 Mar 25 08:29 power
lrwxrwxrwx 1 root root 0 Mar 25 08:29 supplier:platform:pinctrl -> ../../virtual/devlink/platform:pinctrl--platform:ff420020.pwm
drwxr-xr-x 3 root root 0 Feb 27 2024 pwm
lrwxrwxrwx 1 root root 0 Feb 27 2024 subsystem -> ../../../bus/platform
-rw-r--r-- 1 root root 4096 Feb 27 2024 uevent
/sys/devices/platform/ff420020.pwm/power:
total 0
-rw-r--r-- 1 root root 4096 Mar 25 08:29 autosuspend_delay_ms
-rw-r--r-- 1 root root 4096 Mar 25 08:29 control
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_active_time
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_status
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_suspended_time
/sys/devices/platform/ff420020.pwm/pwm:
total 0
drwxr-xr-x 3 root root 0 Feb 27 2024 pwmchip0
/sys/devices/platform/ff420020.pwm/pwm/pwmchip0:
total 0
--w------- 1 root root 4096 Mar 25 09:59 export
lrwxrwxrwx 1 root root 0 Mar 25 08:29 device -> ../../../ff420020.pwm
-r--r--r-- 1 root root 4096 Mar 25 08:29 npwm
drwxr-xr-x 2 root root 0 Mar 25 08:29 power
--w------- 1 root root 4096 Mar 25 08:29 unexport
lrwxrwxrwx 1 root root 0 Feb 27 2024 subsystem -> ../../../../../class/pwm
-rw-r--r-- 1 root root 4096 Feb 27 2024 uevent
/sys/devices/platform/ff420020.pwm/pwm/pwmchip0/power:
total 0
-rw-r--r-- 1 root root 4096 Mar 25 08:29 autosuspend_delay_ms
-rw-r--r-- 1 root root 4096 Mar 25 08:29 control
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_active_time
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_status
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_suspended_time
# ls -lRt /sys/class/pwm/pwmchip0/
/sys/class/pwm/pwmchip0/:
total 0
--w------- 1 root root 4096 Mar 25 09:59 export
lrwxrwxrwx 1 root root 0 Mar 25 08:29 device -> ../../../ff420020.pwm
-r--r--r-- 1 root root 4096 Mar 25 08:29 npwm
drwxr-xr-x 2 root root 0 Mar 25 08:29 power
--w------- 1 root root 4096 Mar 25 08:29 unexport
lrwxrwxrwx 1 root root 0 Feb 27 2024 subsystem -> ../../../../../class/pwm
-rw-r--r-- 1 root root 4096 Feb 27 2024 uevent
/sys/class/pwm/pwmchip0/power:
total 0
-rw-r--r-- 1 root root 4096 Mar 25 08:29 autosuspend_delay_ms
-rw-r--r-- 1 root root 4096 Mar 25 08:29 control
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_active_time
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_status
-r--r--r-- 1 root root 4096 Mar 25 08:29 runtime_suspended_time
Br
Ok, I found a one-liner which kinda seems to be doing the job
pkill -f "gpioset *.*c 4 18 1" ; gpioset -t 300us,100us -c 4 -z 18=1
First off this kills any previous gpioset command on the relevant gpio-pin since you cannot “overwrite” a running process by creating a new one on the same pin.
Then this apparently sends a signal each 300µs followed by another signal 100µs later with the t-flag and demonizes it with the -z-flag, and this is what seems to be called software PWM which shows in htop where it seems to linger somewhere between 4 and 6% CPU.
This (I think) makes up a generated PWM signal of 25kHz with 25% duty cycle (sources wikipedia, Noctua PWM whitepaper, gpioset man-page).
As far as I can tell the pin 11 and 13 are supposed to have hardware PWM which does not put load on the CPU but this seem to not be exposed in the OS.
Looking through the device-tree files in the linux kernel I cannot find any reference to fan or pwm-fan in any relevant files for the Rock 4 SE. Is this by design or is there a reason for this?
Looking at other files, such as the rk3399-khadas-edge.dtsi I see a part that looks promising:
fan: pwm-fan {
compatible = "pwm-fan";
cooling-levels = <0 150 200 255>;
#cooling-cells = <2>;
fan-supply = <&vsys_5v0>;
pwms = <&pwm0 0 40000 0>;
};
or this from rk3399-rockpro64.dtsi:
fan: pwm-fan {
compatible = "pwm-fan";
cooling-levels = <0 100 150 200 255>;
#cooling-cells = <2>;
fan-supply = <&vcc12v_dcin>;
pwms = <&pwm1 0 50000 0>;
};
But nowhere in the following files is anything similar present:
I have grepped through all files in the linux/arch/arm64/boot/dts/rockchip-folder in multiple releases from 5.1 until 6.14 but there does not seem to ever have been any file (of the above) that ever had this option.
Is PWM handled differently somehow for the Rock 4 SE or is there some other kernel to be used rather than the official linux kernel? I have also looked through the repos at Radxa github and rockhip github but cannot find any difference there. It feels like there are device-tree properties missing that should be added.
@alberto Which OS/version did you write the script for?