On Thursday, May 08, 2014 10:17:50 PM Rafael J. Wysocki wrote: > On Thursday, May 08, 2014 10:57:36 AM Alan Stern wrote: > > On Thu, 8 May 2014, Rafael J. Wysocki wrote: > > > > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > > > > Currently, some subsystems (e.g. PCI and the ACPI PM domain) have to > > > resume all runtime-suspended devices during system suspend, mostly > > > because those devices may need to be reprogrammed due to different > > > wakeup settings for system sleep and for runtime PM. > > > > > > For some devices, though, it's OK to remain in runtime suspend > > > throughout a complete system suspend/resume cycle (if the device was in > > > runtime suspend at the start of the cycle). We would like to do this > > > whenever possible, to avoid the overhead of extra power-up and power-down > > > events. > > > > > > However, problems may arise because the device's descendants may require > > > it to be at full power at various points during the cycle. Therefore the > > > most straightforward way to do this safely is if the device and all its > > > descendants can remain runtime suspended until the resume stage of system > > > resume. > > > > > > To this end, introduce dev->power.leave_runtime_suspended. > > > If a subsystem or driver sets this flag during the ->prepare() callback, > > > and if the flag is set in all of the device's descendants, and if the > > > device is still in runtime suspend at the beginning of the ->suspend() > > > callback, that callback is allowed to return 0 without clearing > > > power.leave_runtime_suspended and without changing the state of the > > > device, unless the current state of the device is not appropriate for > > > the upcoming system sleep state (for example, the device is supposed to > > > wake up the system from that state and its current wakeup settings are > > > not suitable for that). Then, the PM core will not invoke the device's > > > ->suspend_late(), ->suspend_irq(), ->resume_irq(), ->resume_early(), or > > > ->resume() callbacks. Instead, it will invoke ->runtime_resume() during > > > the device resume stage of system resume. > > > > Wait a minute. Following ->runtime_suspend(), you are going to call > > ->suspend() and then ->runtime_resume()? That doesn't seem like what > > you really want; a ->suspend() call should always have a matching > > ->resume(). > > Yes, it should, but I didn't see any other way to do that. Actually, that's kind of easy to resolve. :-) When ->suspend() leaves power.leave_runtime_suspended set, the PM core can simply skip the early/late and noirq callbacks and then call ->resume() that will be responsible for using whatever is necessary to resume the device. And perhaps the flag should be called something different then, like direct_resume (meaning go directly for ->resume() without executing the intermediate callbacks)? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
