On Tue, May 04, 2010 at 09:51:39AM -0400, Alan Stern wrote: > On Tue, 4 May 2010, Matthew Garrett wrote: > > On Mon, May 03, 2010 at 04:37:22PM -0700, Kevin Hilman wrote: > > > Please forgive the ignorance of ACPI (in embedded, we thankfully live > > > in magical world without ACPI) but doesn't that already happen with > > > CPUidle and C-states? I think of CPUidle as basically runtime PM for > > > the CPU. IOW, runtime PM manages the devices, CPUidle manages the CPU > > > (via C-states), resulting in dynaimc PM for the entire system. What > > > am I missing? > > ACPI doesn't provide any functionality for cutting power to most devices > > other than shifting into full system suspend. The number of wakeup > > events available to us on a given machine is usually small and the > > wakeup latency large, so it's not terribly practical to do this > > transparently on most hardware. > Another thing that Kevin is missing: There is more to the system than > the devices and the CPU. For example: RAM, an embedded controller (on > modern desktop/laptop systems), a power supply, and so on. Dynamic PM > for the CPU and the devices won't power-down these things, but system > PM will. In an embedded system I'd expect that these other system devices would fall naturally out through the management of the CPUs and devices - for example, the drivers for the individual devices could use the regulator API to manage their supplies and runtime PM is being used to manage CPU core stuff - or could at least readily be handled in a similar fashion. This isn't to say that we're there yet from an implementation point of view, of course. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
