pm - Power Management properties
The pm-hardware-state property can be used to influence the behavior of the Power Management framework. Its syntax and interpretation is described below.
Note that this property is only interpreted by the system immediately after the device has successfully attached. Changes in the property made by the driver after the driver has attached will not be recognized.
pm-hardware-state is a string-valued property. The existence of the pm-hardware-state property indicates that a device needs special handling by the Power Management framework with regard to its hardware state.
If the value of this property is needs-suspend-resume, the device has a hardware state that cannot be deduced by the framework. The framework definition of a device with hardware state is one with a reg property. Some drivers, such as SCSI disk and tape drivers, have no reg property but manage devices with “remote” hardware. Such a device must have a pm-hardware-state property with a value of needs-suspend-resume for the system to identify it as needing a call to its detach(9E) entry point with command DDI_SUSPEND when system is suspended, and a call to attach(9E) with command DDI_RESUME when system is resumed. For devices using original Power Management interfaces (which are now obsolete) detach(9E) is also called with DDI_PM_SUSPEND before power is removed from the device, and attach(9E) is called with DDI_PM_RESUME after power is restored.
A value of no-suspend-resume indicates that, in spite of the existence of a reg property, a device has no hardware state that needs saving and restoring. A device exporting this property will not have its detach() entry point called with command DDI_SUSPEND when system is suspended, nor will its attach() entry point be called with command DDI_RESUME when system is resumed. For devices using the original (and now obsolete) Power Management interfaces, detach(9E) will not be called with DDI_PM_SUSPEND command before power is removed from the device, nor attach(9E) will be called with DDI_PM_RESUME command after power is restored to the device.
A value of parental-suspend-resume indicates that the device does not implement the detach(9E) DDI_SUSPEND semantics, nor the attach() DDI_RESUME semantics, but that a call should be made up the device tree by the framework to effect the saving and/or restoring of hardware state for this device. For devices using original Power Management interfaces (which are now obsolete), it also indicates that the device does not implement the detach(9E) DDI_PM_SUSPEND semantics, nor the attach(9E) DDI_PM_RESUME semantics, but that a call should be made up the device tree by the framework to effect the saving and/or restoring the hardware state for this device.
See attributes(7) for descriptions of the following attributes:
Writing Device Drivers