@RobertCNelson Ok with some trial and error and a fair bit of head scratching I managed to make this work. I have attached the devicetree overlay file I currently have running.
To work though, the udev rule that automatically exports the PWM’s needs to be disabled.
If ehrpwm3 is exported the pwm-fan driver fails as the device is busy.
I removed 81-pwm-noroot.rules from /etc/udev/rules.d to start, then spent 5 minutes wondering why it was still being exported. Removed it from initrd and then the pwm-fan driver loaded and worked.
Heated up my heatsink with a hot air gun to make it change states and it seems to work.
Of course the downside to using the pwm-fan driver is that if you want to modify the fan settings you need to modify the overlay and reboot.
Using the exported PWM device does make this easier, although you then need some sort of script to poll the temperatures and adjust the fan speed.
BONE-FAN.zip (932 Bytes)