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.
>
Ok, so the sysfs don't contain all the dependenceis but dmp_list contains
the exaclty suspend order of the device
> 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.
>
Ok, I understand, so how to know the devices dependences? There is a way
to express
this relation? Because if it is not possible a single flag can be used
>
>> 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.
>
Yes this is possible, but you walk all list twice.
Regards Michael
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