New PWM cooling fan overlay for Pi 3/4 #6571
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Added new overlay pwm-gpio-fan to support a GPIO connected PWM cooling fan controlled by the software-based GPIO PWM kernel module. Signed-off-by: Kai-Uwe Herbing <[email protected]>
Updated README for new pwm-gpio-fan overlay Signed-off-by: Kai-Uwe Herbing <[email protected]>
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This is my 2nd attempt, to make a pull request on the topic. I got stuck with your workflow scripts, that always checked older commits and failed with errors, so I started over again. Please bear with me, as I am entirely new to github and still on a learning curve. I you have an advice how to fix workflow errors with newer commits, without the need to start all over again, I greatly appreciate to learn.
I recently discovered that there is a new kernel based software PWM solution available since November 2024. A software-based PWM kernel module is available since then, back-ported from the Linux kernel 6.11 to the Raspberry Pi OS Bookworm kernel 6.6.62. This made me write a new pwm-gpio-fan overlay for my own use and after extensive testing on a Pi 3, I have published it for the community.
Moderator 6by9 on the Raspberry Pi forum suggested that I make a pull request, so that it gets merged for all Pi users.
Using the new kernel-based software PWM imposes several advantages over other implementations I have found on the internet and this forum:
Compared with the existing gpio-fan overlay, the fan runs much quieter, often not even noticeable, due to the use of real PWM duty cycles.
No hardware PWM (PWM0 or PWM1) of the Pi is occupied, so there is no conflict with the Pi's analogue audio output anymore.
Reliable on even high CPU loads, as it's part of the kernel.
Doesn't consume noticeable CPU power even on a Pi 3.