On Tuesday, November 26, 2013 04:09:44 PM Alan Stern wrote: > On Tue, 26 Nov 2013, Rafael J. Wysocki wrote: > > > On Tuesday, November 26, 2013 10:48:56 AM Ulf Hansson wrote: > > > On 26 November 2013 00:10, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > > > On Monday, November 25, 2013 01:40:21 PM Ulf Hansson wrote: > > > >> To put devices into low power state during sleep, it sometimes makes > > > >> sense at subsystem-level to re-use device's runtime PM callbacks. > > Ulf, please be more careful about the distinction between "device" and > "driver". Devices don't have callbacks; drivers do. You made this > mistake a few times in the patch description. > > > > >> The PM core will at device_suspend_late disable runtime PM, after that > > > >> we can safely operate on these callbacks. At suspend_late the device > > > >> will be put into low power state by invoking the device's > > > >> runtime_suspend callback, unless the runtime status is already > > > >> suspended. At resume_early the state is restored by invoking the > > > >> device's runtime_resume callback. Soon after the PM core will re-enable > > > >> runtime PM before returning from device_resume_early. > > > >> > > > >> The new pm_generic functions are named pm_generic_suspend_late_runtime > > > >> and pm_generic_resume_early_runtime, they are supposed to be used in > > > >> pairs. > > > > > > > > What happens if the subsystem uses the new functions as its late suspend/ > > > > early resume callbacks, but some of its drivers implement .suspend_late() > > > > and .resume_early()? > > The same thing that happens whenever any PM-related callback is defined > by both the subsystem and the driver: The PM core uses the subsystem's > callback. (Or the pm_domain's callback, or the type's callback, or the > class's callback.) Precisely. But my question was more about how we are going to indicate it to the driver writers (who may not be familiar with that subsystem to start with and may have experience with some other subsystems that don't use these new functions) that they are not supposed to populate .suspend_late and .resume_early. > Besides, Ulf specifically assumed at the top of this message that > re-using the runtime-suspend callback makes sense at the subsystem > level. This must mean it is appropriate for all drivers in the > subsystem. So why would a driver want to override the subsystem's > behavior? By mistake? > > > Good point. Normally, I think the decision of using these callbacks > > > should be taken at the lowest level, in other words in the driver. > > > Otherwise the lowest layer of .suspend_late will be by-passed. > > > > I'm not sure what's the point to add them, then. If the driver has to decide > > anyway, it may simply populate its .suspend_late and .resume_early pointers > > I think. > > Another possibility is to have the pm_generic_suspend_late_runtime > routine check to see if the driver has defined a suspend_late callback. > If the driver has its own callback, we could invoke it instead of > invoking the runtime_suspend callback. > > However, I'm not sure that doing this would be worthwhile. And it > would hang in an infinite loop if the driver set its suspend_late > pointer to pm_generic_suspend_late_runtime! Well, that's supposed to be a subsystem-level callback. Anyway, my personal opinion is that we seem to be adding confusion instead of reducing it here ... Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
