int ddi_dev_is_needed(dev_info_t *dip, int component, int level);
ddi_dev_is_needed(9F) is called when the driver discovers that a component needed for some operation has been powered off. This interface arranges for the driver to be called to set the current power level of the component to the level specified in the request. All the devices that depend on this component are also brought back to normal power by this call.
When a component has been powered off by pm(7D) and a request or interrupt occurs that requires the component to be powered up, the driver must call ddi_dev_is_needed(9F) so that the framework can restore the component (and all of the devices that depend on it) to normal power.