On Tuesday 17 February 2009, Alan Stern wrote: > On Tue, 17 Feb 2009, Rafael J. Wysocki wrote: > > > On Monday 16 February 2009, Alan Stern wrote: > > > On Mon, 16 Feb 2009, Rafael J. Wysocki wrote: > > > > > > > OK, so I think there are two things that user space may be allowed to do as > > > > far as putting devices into low power states is concerned: > > > > * disable/enable the automatic power management of the device (provided that > > > > the driver supports the automatic PM) > > > > > > Set the automatic PM parameters (idle timeout, state to go to, etc.). > > > > Yes. I'm not sure about the state part, though. > > Maybe, maybe not. IMO it's too early to tell whether anyone will need > this ability, so we shouldn't rule it out. > > > > What about situations where we want to distinguish between the power > > > state of the device itself and the power state of the link? For a disk > > > drive we may want to power the link on and off quite a lot, as that > > > has low latency, but spinning the disk up and down takes a long time > > > and so should have a longer idle-time value. > > > > Well, I'm not sure at the moment. > > > > Do you have any suggestions? > > Not very well fleshed-out ones. I've got a vague idea for allowing a > disk to have a 3-level power arrangement: full power, link disabled but > drive still spinning, and device suspended. I was thinking about that too. > Arranging for automatic transitions among those states will be a little > clumsy but it can be done. As an example of the clumsiness, this scheme > requires that the drive has _two_ idle-timeout values, one for the link and > one for the drive itself. Well, this generally is the case for PCI devices supporting more than two power states. > Another possibility is to set up independent runtime PM for the > transport and the device. This means allowing the possibility that the > transport is suspended while its child (the device) is not. This is a > little simpler (there's only one idle-timeout per device, since the > link is treated as an independent device), but it violates the > principle of never suspending a parent while there is an active child. Well, I think the first approach would be better. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
