On Tue, 13 Nov 2012, Huang Ying wrote: > > This is not quite right. Consider a device that is in runtime suspend > > when a system sleep starts. When the system sleep ends, the device > > will be resumed but the PM core will still think its state is > > SUSPENDED. The subsystem has to tell the PM core that the device is > > now ACTIVE. Currently, subsystems do this by calling > > pm_runtime_disable, pm_runtime_set_active, pm_runtime_enable. Under > > your scheme this wouldn't work; the pm_runtime_set_active call would > > fail because the device was !forbidden. > > Thanks for your information. For this specific situation, is it > possible to call pm_runtime_resume() or pm_request_resume() for the > device?
No, because the device already is at full power. The subsystem just needs to tell the PM core that it is. > > > PM. Device can always work with full power. > > > > It can't if the parent is in SUSPEND. If necessary, the user can write > > "on" to the parent's power/control attribute first. > > Is it possible to call pm_runtime_set_active() for the parent if the > parent is disabled and SUSPENDED. Doing that is possible, but it might not work. The parent might actually be at low power; calling pm_runtime_set_active wouldn't change the physical power level. Basically, it's not safe to assume anything about devices that are disabled for runtime PM. > It appears that there is race condition between this and the > pm_runtime_disable, pm_runtime_set_active, pm_runtime_enable sequence > you mentioned ealier. > > thread 1 thread 2 > pm_runtime_disable > pm_runtime_set_active > pm_runtime_allow > pm_runtime_set_suspended > pm_runtime_enable This can't happen in the situation I described earlier because during system sleep transitions, no other user threads are allowed to run. All of them except the one actually carrying out the transition are frozen. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
