At its current state, the GPIO driver doesn't have feedback support, If someone know how it work on driver level, that could be cool 
On the hardware level, it is pretty easy, you need a GPIO input, a resistor and a NPN transistor.
I use this to control the fan in one of my build:
1x MMBT2222A SOT23
1x 1206 470ohm resistor, this value can be increase but I don't know the right calculation for this
On the hardware level, it is pretty easy, you need a GPIO input, a resistor and a NPN transistor.
I use this to control the fan in one of my build:
1x MMBT2222A SOT23
1x 1206 470ohm resistor, this value can be increase but I don't know the right calculation for this