On Sun, 8 Apr 2012, Kevin Cernekee wrote: > In embedded applications, there are a number of situations in which it > is useful to completely disable a host controller in order to conserve > power. Some typical scenarios include: <SNIP> > Looking through Linus' head of tree, I see: > > USB runtime PM seems to focus on the individual USB devices, and does > not allow for dynamically suspending the entire host controller > AFAICT. That is not correct. USB host controllers _can_ be suspended. (Not all of them; many of the platform drivers don't implement controller suspend. But some of them do, and almost all of the PCI-based drivers do.) > USB used to allow writing "suspend" to the power/control file, but > that no longer seems to be the case as of 2.6.32. Correct. > In general I don't > see any facility where the application can explicitly tell the PM core > to suspend a device (incurring a potential loss of functionality, such > as hot plug/unplug detection). Right; there is no way to do this. The OS will suspend a device only when it believes it is safe to do so. <SNIP> > So, my questions are: > > a) Is SATA/USB/MMC host controller suspension something that can be > accomplished within the existing runtime PM framework? Not only _can_ it be accomplished, it already _has_ been accomplished (for USB at least, I'm not familiar with the others). > b) If not, what is the best way to modify the runtime PM framework so > that it can support these use cases? No changes to the framework are needed. If a subsystem or driver doesn't support runtime suspend then support has to be added at the subsystem or driver level. > c) Is this something you would even want in mainline? Yes. People are already working on this stuff. > d) Or should I just go back to using "rmmod"? I don't see how rmmod will save any power. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
