Linux supports a wide variety of hardware, each with different power management characteristics and capabilities. However, power management statistics (e.g. calling a power tick for determining an idling) are generally gathered at the class device level. In order for class devices to relate bus specific power states to their own state change intentions, it may make sense to have a table mapping each bus level power state to its corresponding generic Linux power state. Another problem with having multiple separate states is that it is very difficult to relate the power requirements of child devices when the parent has a different set of bus level power states. I would like to explore the possibility of defining a set of generic power states, to which each bus level state can be mapped. It might be as follows: functional - the device is operational. context - the current data/operations passing through the device configuration - resources, firmware, settings done in *probe, etc. POWER_ON: the device is fully functional POWER_LIGHT: device context and configuration are maintained, but device isn't functional. POWER_MODERATE: device configuration is maintained, but the context is not. The device isn't functional POWER_DEEP: no device configuration or context is maintained, but device is not fully off. The device is not functional. POWER_OFF: no power is applied to the device. The device is not functional. Each lower state would save more power, but also require more latency when returning to "POWER_ON". When a device is in one of the above specific power mode classes, it's up to the device driver to control more fine grained power transitions. Comments? Thanks, Adam
