Multiple Power Management Components

To the power management framework, all components are considered equal and completely independent of each other. If this is not true for a particular device, the device driver must ensure that undesirable state combinations do not occur. For example, with a frame buffer/monitor card with a monitor attached to it, for each possible power state of the monitor (On, Standby, Suspend, Off) there are states of the frame buffer electronics (D0, D1, D2, D3) that are not allowed if the device is to work properly. If the monitor is On, then the frame buffer must be at D0 (full on), so if the frame buffer driver gets a request to power up the monitor to On while the frame buffer is D3, it must ask the system to bring the frame buffer back up (by calling pm_raise_power(9F)) before setting the monitor On. If the frame buffer driver gets a request from the system to lower the power of the frame buffer while the monitor is On, it must fail that request.