Writing Device Drivers

Changes to Power Management Interfaces

Previous to the Solaris 8 release, power management of devices was not automatic. It was necessary to add an entry to /etc/power.conf for each device that was to be power managed.

The framework assumed that all devices supported only two power levels: 0 and full (“normal”) power.

There was an implied dependency of all other components on component 0. Whenever component 0 changed to or from level 0, a call was made into the driver's detach(9E) or attach(9E) routine with commands DDI_PM_SUSPEND and DDI_PM_RESUME respectively to save and restore hardware state.

The old interfaces (including ddi_dev_is_needed(9F), pm_create_components(9F), pm_destroy_components(9F), pm_get_normal_power(9F), pm_set_normal_power(9F), DDI_PM_SUSPEND and DDI_PM_RESUME) are still supported for binary compatibility, but are obsolete.

As of the Solaris 8 release, devices which export the pm-components property are automatically power managed (if autopm is enabled).

The framework now knows from the pm-components property which power levels are supported by each device.

The framework makes no assumptions about dependencies among the different components of a device. The device driver is responsible for saving and restoring hardware state as needed when changing power levels.

These changes allow the power management framework to deal with emerging device technology, and result in greater power savings (since the framework can detect automatically which devices can save power, and can use intermediate power states of the devices), and allows the system to meet energy consumption goals without the entire system being powered down or functionality being lost.

Table 9–1 Power Management Interfaces

Old Interfaces 

Solaris 8 Interfaces