Busy-Idle State Transitions

The driver must keep the framework informed of device state transitions from idle to busy or busy to idle. Where these transitions happen is entirely device-specific. The transitions from idle to busy and from busy to idle depend on the nature of the device and the abstraction represented by the specific component. For example, SCSI disk target drivers typically export a single component, which represents whether the SCSI target disk drive is spun up or not. It is marked busy whenever there is an outstanding request to the drive and idle when the last queued request finishes. Some components are created and never marked busy (components created by pm-components(9P) are created in an idle state).

The pm_busy_component(9F) and pm_idle_component(9F) interfaces notify the power management framework of busy-idle state transitions. The syntax for pm_busy_component(9F) is:

    int pm_busy_component(dev_info_t *dip, int component);

pm_busy_component(9F) marks component as busy. While the component is busy, it will not be powered off. If the component is already powered off, then marking it busy doesn't change its power level. The driver needs to call pm_raise_power(9F) for this purpose. Calls to pm_busy_component(9F) are cumulative and require a corresponding number of calls to pm_idle_component(9F) to idle the component.

The syntax for pm_idle_component(9F) is:

int pm_idle_component(dev_info_t *dip, int component);

pm_idle_component(9F) marks component as idle. An idle component is subject to being powered off. pm_idle_component(9F) must be called once for each call to pm_busy_component(9F) in order to idle the component.