Start work on a driver for the AMD SMU (system management unit), which will eventually be used for getting S0ix statistics (e.g. how long the CPU has spent in the deepest - S0i3 - sleep state during the last sleep) as well as letting PMFW (power management firmware, running on the SMU) know when we intend to enter and exit sleep. It is what's responsible for turning off the VDD line to the CPU.
Currently, amdsmu is just able to get the SMU's firmware version on AMD Rembrandt, Phoenix, and Strix Point CPUs. Future patches will come for stats and sleep, and will hopefully help with the EC wake event "noisiness" issue described in D48387.
This is the equivalent to amd-pmc on Linux.