power()

	int xxpower(dev_info_t *dip, int component, int level);

The system calls the power(9E) entry point (either directly or as a result of a call to ddi_dev_is_needed(9F)) when it determines that a component's current power level needs to be changed. The action taken by this entry point is device driver specific. In the example of the SCSI target disk driver mentioned previously, setting the power level of the component to 0 results in sending a SCSI command to spin down the disk, while setting the power level to the normal power level results in sending a SCSI command to spin up the disk. Example 8-1 shows a sample power(9E) routine.

Example 8-1 power(9E) Routine

int
xxpower(dev_info_t *dip, int component, int level)
{
  	struct xxstate *xsp;
	   int	instance;
	   instance = ddi_get_instance(dip);
  	xsp = ddi_get_soft_state(statep, instance);

	   /*
	   * Make sure that the request is valid
  	*/
 	if (xx_valid_power_level(component, level))
	    	return (DDI_FAILURE);

 	mutex_enter(&xsp->mu);
 	if (xsp->xx_power_level[component] != level) {
	    	device- and component-specific setting of power level.
	    	xsp->xx_power_level[component] = level;
 	}
 	mutex_exit(&xsp->mu);
 	return (DDI_SUCCESS);
}