SCMI and ACPI
SCMI has good capabilitiy with ACPI.
SystemReady does not mandate any power methods.
No perfect device exist today for client PC power management related work. Juno is outdated.
SCMI interface could be emulated in TF-A. QEMU could be potentially used to build an emulated platform with acpi power methods and capabilities to validate the software stack.
Lorenzo can put the details (e.g: what needs to be emulated etc.) on confluence and Shashi can identify if anymore work is required on QEMU to support that.