MJG wrote "a new type of power controller, for instance, you need to add a driver for that to the OS"....
With all due respect, I think that is wrong. In the x86 PC example, power management could be done via a generic interface on I/O Ports. As an example, the generic power management specification specifies what I/O Port read/writes will cause computer to go to S3 Suspend-To-RAM. For a "new power controller", it will have to follow the specification above. I believe ACPI instead has a complex AML interpreter to basically allow different I/O Port / memory accesses for different devices that do the same function! ACPI is poorly designed.
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With all due respect, I think that is wrong.
In the x86 PC example, power management could be done via a generic interface on I/O Ports.
As an example, the generic power management specification specifies what I/O Port read/writes will cause computer to go to S3 Suspend-To-RAM.
For a "new power controller", it will have to follow the specification above.
I believe ACPI instead has a complex AML interpreter to basically allow different I/O Port / memory accesses for different devices that do the same function! ACPI is poorly designed.