> I think both Patrick Mochel and Alan Stern have sent patches at > various times to let individual drivers provide a list of named > states they support, In some cases (like PCI) those lists could > be delegated to bus-specific code. I've several times expressed my opinion there that it's not bus states that should be exposed by a driver but the actual states that the driver/device combination supports _regardless_ of what bus state they map to (if any). Bus states simply mean nothing at this point (Unless you are the bus driver). Of course we need both top-down and bottom-up dependency mecanisms to handle state changes, but at the user level, a given PCI driver shouldn't expose something like "D1", "D2" and "D3"... those are PCI states that don't have a well defined semantics (and may not be all supported by the device/driver). However, it's whatever functional states that device/driver supports that shall be exposed. Those can be "idle" and "suspended" for example, or there could be several levels of "suspended". Now of course, there is the problem that while such descriptive names might have a sense to a user (and even then, only in one language, english) they aren't very useful to some automated power management mecanism. That's the whole problem that needs solving, possibly by exposing as much as the state dependencies as possible, along eventually with informations such as can the device automatically trigger a transition out of this state, eventually informations relative to max power consumed in this state (not only embedded devices but also desktop machines nowadays have fairly strick power budgets when entering global system suspend), etc... That was one of the goal of the mecanisms I described more than a year ago with bit masks exposing bus state <-> device state dependencies, though not a complete solution, it was more like a starting point to think from. Due to various personal matter I haven't followed up much on what came next on this list or during the last PM summit, but from some of the mails I'm reading, I have the feeling that there haven't been much progress... Ben
