On Monday 09 February 2009, Alan Stern wrote: > On Sun, 8 Feb 2009, Arve Hjønnevåg wrote: > > > How do you handle devices that should be in a low power mode when > > closed, and a high(er) power mode when open. While adding > > early-suspend hooks to a driver may be ugly, it does not need any more > > support than open and close does. > > This illustrates some of the problems of differing outlooks. In an > embedded system, the set of devices is limited and the set of available > power states is known beforehand. In other settings neither of these > is true. > > Early-suspend is an example of a partially-functional system state. > In your Android-centric approach, early-suspend is centered around the > screen. But other sorts of systems way well have other requirements > and may want their partially-functional system state to be centered > around something else. Or they may want to have more than one > partially-functional system state. > > What we need is a mechanism capable of accomodating all these different > requirements. Presumably the core kernel would provide the hooks but > the implementation details would be left up to platform-specific code. > There should be a generic scheme for representing partially-functional > system states, together with a list of devices to be put in low-power > mode for each state and an indication of which low-power mode to use > (since a device can have more than one low-power mode). Device drivers > should have an interface for going into a particular low-power state. > > The extent to which all of this needs to be split between the kernel > and userspace isn't immediately clear. Latency issues might force a > large part of it to live in the kernel. On the other hand, if the list > of devices & modes can be pushed out to userspace, then the in-kernel > portion could end up being nothing more than a runtime-PM mechanism of > the sort we have been discussing for years. Agreed. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
