When a subsystem requires a device node, either peripheral or memory, the device must be requested using the power management API. After the device node has performed its function and is no longer required, it should be released, so the device can be powered off or used by other subsystems.
When you call the
the platform management firmware turns off devices (such as a peripheral or memory) that
are not requested by any subsystem.
You must pass the PM_CAP_ACCESS argument to the REQUEST_NODE API to access the particular peripheral/memory, as otherwise it is not powered ON.
The device, clock, and the reset operation are also not allowed if the device is not requested.