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

pm_power_has_changed - Notify Power Management framework of autonomous power level change

#include <sys/ddi.h>
#include <sys/sunddi.h>
int pm_power_has_changed(dev_info_t *dip, int component, int level);

illumos DDI specific (illumos DDI)

Pointer to the device dev_info structure


Number of the component that has changed power level


Power level to which the indicated component has changed

The pm_power_has_changed(9F) 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 autonomous 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).

The pm_power_has_changed() function returns:


The power level of component was successfully updated to level.


Invalid component component or power level level.

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.

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

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.
	if (level_informed == *(xsp->level_reg_addr)) {
		if (pm_power_has_changed(xsp->dip, XXUSB_COMPONENT,
		    level_informed) != DDI_SUCCESS) {
			mutex_exit( &xsp->lock);
xxdisk_power(dev_info *dip, int comp, int level)
	mutex_enter( xsp->lock);

See attributes(7) for a description of the following attributes:

Interface Stability Committed

pm(4D), power.conf(5), attach(9E), detach(9E), power(9E), pm_busy_component(9F), pm_idle_component(9F), pm_lower_power(9F), pm_raise_power(9F), pm(9P), pm-components(9P)

Writing Device Drivers

July 22, 2004 OmniOS