On Thursday 23 July 2009, Michael Trimarchi wrote:
> Hi all,
>
> Alan Stern wrote:
> > On Sat, 25 Apr 2009, Michael Trimarchi wrote:
> >
> >
> >> Anyway, I revert this beacuse is wrong but is it correct to use here the
> >> list_add instead the list_add_tail, it put the child node
> >> after the parent stricly and don't create hole in subtree visit. Now I
> >> see only a dump
> >> reason for debugging and a simple exit in flag update.
> >> The important thing is that the children follow the parent,
> >> and in this way is like visiting the tree.
> >>
> >
> > That's not necessarily true. There may be dependencies between devices
> > that aren't expressed by the parent-child relationship.
> >
> > For example, device B might require device A even though A isn't a
> > parent (or ancestor) of B. The way dpm_list works now this is okay,
> > because devices are added in order of discovery. That is, if B depends
> > on A then A must have been discovered before B, so A will come first on
> > the list.
> >
> > If you change things by adding children directly after their parent
> > then you will mess this up. For example, if B's parent was discovered
> > before A, then adding B directly after its parent would mean putting B
> > before A on the list. Then you'd run into trouble during a system
> > suspend, because A would be suspended before B and that would prevent B
> > from working properly.
> >
> >
> >> Nothing change for me because
> >> is difficult
> >> to isolate only a subtree, if you have a list, but I'm sure that if I
> >> find a subtree with
> >> the same parent, my subtree is finish, and if someone add a new device,
> >> the system put
> >> in the correct position.
> >>
> >
> > It is _not_ difficult to isolate a subtree using a list. For example:
> >
> > mutex_lock(&dpm_mutex);
> > topdev->in_subtree = 1;
> > list_for_each_entry(dpm_list, dev, power.entry) {
> > if (dev->parent && dev->parent->in_subtree)
> > dev->in_subtree = 1;
> > }
> > list_for_each_entry(dpm_list, dev, power.entry) {
> > if (dev->in_subtree) {
> > dev->in_subtree = 0;
> > dev->dont_suspend = 1;
> > }
> > }
> > mutex_unlock(&dpm_mutex);
> >
> > This will set the dont_suspend flag for all devices in the subtree
> > starting at topdev.
> >
> > Alan Stern
> >
> I follow the discussion around the new runtime support and I would like
> to know if I can
> add to the new interface the no_suspend flag or maybe now there is a
> better solution.
Hmm. Do I remember correctly that the no_suspend flag is for preventing the
system-wide suspend in case some devices are in use?
Rafael
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