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
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