I recently worked on bringing Runtime Power Management support to the Raspberry Pi V3D driver.

The plan sounded simple: turn the GPU clock off when the GPU is idle. But this ended up involving firmware-managed clocks, power domains, runtime handling, and a few “why is this still on?” moments.

Check out the details of the implementation and the idle power savings in this blog post:

https://mairacanal.github.io/bringing-runtime-pm-to-raspberry-pi-gpu/