pm_power_has_changed(9F)				   Kernel Functions for Drivers 				  pm_power_has_changed(9F)

NAME

       pm_power_has_changed - Notify Power Management framework of autonomous power level change

SYNOPSIS

       #include <sys/ddi.h>
       #include <sys/sunddi.h>

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

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI)

PARAMETERS

       dip	       Pointer to the device dev_info structure

       component       Number of the component that has changed power level

       level	       Power level to which the indicated component has changed

DESCRIPTION

       The  pm_power_has_changed(9)  function  notifies  the  Power  Management framework that the power level of component of dip  has changed to
       level.

       Normally power level changes are initiated by the Power Management framework due to device idleness, or through a request to the  framework
       from  the  driver via pm_raise_power(9F) or pm_lower_power(9F), but some devices may change power levels on their own. For the framework to
       track the power level of the device under these circumstances, the framework must be notified of autonomous power level changes by  a  call
       to pm_power_has_changed().

       Because of the asynchronous nature of these events, the Power Management framework might have called power(9E) between the device's autono-
       mous power level change and the driver calling pm_power_has_changed(), or the framework may be in the process of changing the  power  level
       when  pm_power_has_changed()  is  called.  To  handle these situations correctly, the driver should verify that the device is indeed at the
       level or set the device to the level if it doesn't support inquirying of power levels, before calling pm_power_has_changed(). In  addition,
       the driver should prevent a power(9E) entry point from running in parallel with pm_power_has_changed().

       Note -  If  this  function  is called as a result of entry into the driver's attach(9E), detach(9E) or power(9E) entry point, this function
	       must be called from the same thread which entered attach(9E), detach(9E) or power(9E).

RETURN VALUES

       The pm_power_has_changed() function returns:

       DDI_SUCCESS     The power level of component was successfully updated to level.

       DDI_FAILURE     Invalid component component or power level level.

CONTEXT

       This function can be called from user or kernel context. This function can also be called from interrupt context, providing that it is  not
       the first Power Management function called by the driver.

EXAMPLES

       A hypothetical driver might include this code to handle pm_power_has_changed(9):

       static int
       xxusb_intr(struct buf *bp)
       {

	    ...

	    /*
	     * At this point the device has informed us that it has
	     * changed power level on its own. Inform this to framework.
	     * We need to take care of the case when framework has
	     * already called power() entry point and changed power level
	     * before we were able to inform framework of this change.
		* Handle this by comparing the informed power level with
	     * the actual power level and only doing the call if they
	     * are same. In addition, make sure that power() doesn't get
	     * run in parallel with this code by holding the mutex.
	     */
	       ASSERT(mutex_owned(&xsp->lock));
	    if (level_informed == *(xsp->level_reg_addr)) {
		 if (pm_power_has_changed(xsp->dip, XXUSB_COMPONENT,
		     level_informed) != DDI_SUCCESS) {
		      mutex_exit( &xsp->lock);
		      return(DDI_INTR_UNCLAIMED);
		 }
	       }

	    ....

       }

       xxdisk_power(dev_info *dip, int comp, int level)
       {
	    mutex_enter( xsp->lock);

	    ...

	    ...

       }

ATTRIBUTES

       See attributes(5) for a description of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Stability level 	     |Evolving			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       power.conf(4),	 pm(7D),    attach(9E),   detach(9E),	power(9E),   pm_busy_component(9F),   pm_idle_component(9F),   pm_raise_power(9F),
       pm_lower_power(9F), pm(9P), pm-components(9P)

	Writing Device Drivers

SunOS 5.10							   22 July 2004 					  pm_power_has_changed(9F)