Re: parallel suspend/resume

Rafael J. Wysocki
2007-12-08T20:43:25Z

On Saturday, 8 of December 2007, Alan Stern wrote:
> On Sat, 8 Dec 2007, Oliver Neukum wrote:
>
> > Am Freitag, 7. Dezember 2007 19:01:12 schrieb David Brownell:
> > > FWIW the appended patch removes that rude "order of registration"
> > > policy, so that the suspend/resume list matches the device tree.
> > > It's behaved OK on PCs and, in light duty, a few development boards;
> > > I've carried it around most of this year.
> >
> > As it is a tree, why not store it as such?
>
> There's no need to "store" the tree ordering specially, since all the
> pointers already exist. The question is: In what order should the tree
> be traversed? About the only explicit constraint we have now is that
> children must be suspended before their parents, but there undoubtedly
> are plenty of undocumented implicit constraints (maybe some of them
> aren't known to anybody at all).

Yes, that makes me nervous every time someone suggests to change the ordering
of suspending devices.

> Given the vast number of possible orders, and given that the only order
> we _know_ works correctly is reverse order of registration, I don't see
> any big reason to change. Speeding things up by parallel suspension
> would be a valid reason, but it needs to be done with a great deal of
> care.

Agreed.

Greetings,
Rafael