On Mon, 2012-11-12 at 21:32 -0500, Alan Stern wrote:
> On Tue, 13 Nov 2012, Huang Ying wrote:
>
> > Sorry, my original idea is:
> >
> > pm_runtime_disable will put device into SUSPENDED state if
> > dev->power.runtime_auto is clear. pm_runtime_allow will put
> > device into SUSPENDED state if dev->power.disable_depth > 0.
>
> That's close to what I suggested.
>
> > So in general, my original idea is to manage device runtime power state
> > automatically instead of manually, especially when device is in disabled
> > state.
> >
> > disabled + forbidden -> ACTIVE
> > disabled + !forbidden -> SUSPENDED
>
> 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?
> > enabled + forbidden -> ACTIVE
> > enabled + !forbidden -> auto
> >
> > Why we can not do that?
>
> See above. What we can do instead is:
>
> disabled + forbidden -> ACTIVE
> disabled + !forbidden -> anything
>
> which is basically what I proposed.
>
> > > This means:
> > >
> > > pm_runtime_set_suspended should fail if dev->power.runtime_auto
> > > is clear.
> >
> > I think we can WARN_ON() here. Because the caller should responsible
> > for state consistence if they decide to manage runtime power state
> > manually.
>
> No. Drivers should not have to worry about whether runtime PM is
> forbidden. Worrying about that is the PM core's job.
En... It appears that what caller can do is just do not call
pm_runtime_set_suspended() if forbidden. So your method should be
better.
> > > pm_runtime_forbid should call pm_runtime_set_active if
> > > dev->power.disable_depth > 0. (This would run into a problem
> > > if the parent is suspended and disabled. Maybe
> > > pm_runtime_forbid should fail when this happens.)
> >
> > pm_runtime_forbid() may be called via echo "on" > .../power/control. I
> > think it is hard to refuse the request from user space to forbid runtime
> > 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.
> > > Finally, we probably should make a third change even though it isn't
> > > strictly necessary:
> > >
> > > pm_runtime_allow should call pm_runtime_set_suspended if
> > > dev->power.disable_depth > 0.
> >
> > I think this is something similar to manage device power state
> > automatically if disabled.
>
> Yes, it is similar but not exactly the same as your proposal.
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
Best Regards,
Huang Ying
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