On Mon, 2012-11-12 at 11:32 -0500, Alan Stern wrote:
> On Mon, 12 Nov 2012, Huang Ying wrote:
>
> > > > Is it absolute necessary to call pm_runtime_set_suspended? If the
> > > > device is disabled, the transition to SUSPENDED state will not be
> > > > triggered even if the device is ACTIVE.
> > >
> > > It's not absolutely necessary to do this, but we ought to because it
> > > will allow the device's parent to be suspended. If we leave the device
> > > in the ACTIVE state then the parent can't be suspended, even when the
> > > device is disabled.
> >
> > I think this is the hard part of the issue. Now "disabled" and
> > SUSPENDED state is managed by hand. IMHO, if we changed
> > pm_runtime_allow() as you said, we need to change the rule too. Maybe
> > something as follow:
> >
> > - remove pm_runtime_set_suspended/pm_runtime_set_active
>
> We can't remove them entirely. They are needed for situations where
> the device's physical state is different from what the PM core thinks;
> they tell the PM core what the actual state is.
>
> > - in pm_runtime_disable/pm_runtime_allow, put device into SUSPENDED
> > state if runtime PM is not forbidden.
>
> That doesn't make sense. Runtime PM is never forbidden after
> pm_runtime_allow is called; that's its purpose.
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.
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
enabled + forbidden -> ACTIVE
enabled + !forbidden -> auto
Why we can not do that?
> > - in pm_runtime_forbid/pm_runtime_enable, put device into ACTIVE state.
>
> Why should pm_runtime_enable put the device into the ACTIVE state?
>
> No, I think a better approach is simply to say that the device will
> never be allowed to be in the SUSPENDED state if runtime PM is
> forbidden. We already enforce this when the device is enabled for
> runtime PM, so we would have to start enforcing it when the device is
> disabled.
>
> 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.
> 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.
> 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.
Best Regards,
Huang Ying
> Rafael, what do you think?
>
> Alan Stern
>
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