On Tuesday, May 13, 2014 10:49:32 AM Alan Stern wrote: > On Tue, 13 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 complete stage of > > system resume. > > > > To this end, introduce a new device PM flag, power.direct_complete > > and modify the PM core to use that flag as follows. > > > > If the ->prepare() callback of a device returns a positive number, > > the PM core will regard that as an indication that it may leave the > > device runtime-suspended. It will then check if the system power > > transition in progress is a suspend (and not hibernation in particular) > > and if the device is, indeed, runtime-suspended. In that case, the PM > > core will set the device's power.direct_complete flag. Otherwise it > > will clear power.direct_complete for the device and it also will later > > clear it for the device's parent (if there's one). > > > > Next, the PM core will not invoke the ->suspend() ->suspend_late(), > > ->suspend_irq(), ->resume_irq(), ->resume_early(), or ->resume() > > callbacks for all devices having power.direct_complete set. It > > will invoke their ->complete() callbacks, however, and those > > callbacks are then responsible for resuming the devices as > > appropriate, if necessary. > > Perhaps you should mention here (and maybe even as a comment in the > code) that ->complete() callbacks may want to call pm_request_resume() > if dev->power.direct_resume is set, but they shouldn't call > pm_runtime_resume(). OK > > Changelog partly based on an Alan Stern's description of the idea > > (http://marc.info/?l=linux-pm&m=139940466625569&w=2). > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > ... > > > @@ -1518,17 +1527,19 @@ static int device_prepare(struct device > > callback = dev->driver->pm->prepare; > > } > > > > - if (callback) { > > - error = callback(dev); > > - suspend_report_result(callback, error); > > - } > > + if (callback) > > + ret = callback(dev); > > > > device_unlock(dev); > > > > - if (error) > > + if (ret < 0) { > > + suspend_report_result(callback, ret); > > pm_runtime_put(dev); > > - > > - return error; > > + return ret; > > + } > > + dev->power.direct_complete = ret > 0 && state.event == PM_EVENT_SUSPEND > > + && pm_runtime_suspended(dev); > > Shouldn't the flag be set under the spinlock? I guess you're worried about runtime PM flags being modified in parallel to this? But we've just done the barrier a while ago, so is that still a concern here? This won't run in parallel with device_prepare() for any other devices, because the "complete" phase is sequential. 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
