Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive

[Alan Stern]

On Fri, 3 Jul 2015, Tomeu Vizoso wrote:

> >> Yeah, that would remove the need for messing with the runtime PM
> >> enable status of descendant devices, but I wonder why Rafael went that
> >> way initially.
> >
> > I forget the details.  Probably it was just to be safe.  We probably
> > thought that if a device was disabled for runtime PM then its runtime
> > PM status might not be accurate.  But if direct_complete is set then it
> > may be reasonable to assume that the runtime PM status _is_ accurate.
> 
> Cool.

> > Rafael and I briefly discussed ignore_children while the original
> > direct_complete patch was being designed.  We didn't come to any
> > definite conclusion and decided to forget about it for the time being.
> > Maybe now would be a good time to reconsider it.
> 
> I would prefer to have ignore_children ignore whether the children of
> a device were able to do direct_complete, rather than having a
> direct_complete_default flag (plus not requiring that all its
> descendants have runtime PM enabled).

Okay, but remember that sometimes these "virtual" devices will exist 
beneath a device that needs to have ignore_children off.  So this won't 
be a complete solution to your problem.

Let's see what Rafael thinks about these two issues.  It seems to me
that the hardest part is dealing with drivers/subsystems that have no
runtime PM support.  In such cases, we have to be very careful not to
use direct_complete unless we know that the device does no power 
management at all.

Alan Stern

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