On Mon, 10 Oct 2011, Felipe Balbi wrote:
> > > > In fact we do already have sibling lists. They are maintained as part
> > > > of the device_private structure. What we are missing is a
> > > > device_for_each_sibling() routine. It could be added pretty easily; it
> > > > would be similar to device_for_each_child().
> > >
> > > care to point out where is ?
> > >
> > > 68 struct device_private {
> > > 69 struct klist klist_children;
> > > 70 struct klist_node knode_parent;
> > -------------^ Here. The "parent" in the name refers to where the
> > head of the list is stored.
> >
> > > 71 struct klist_node knode_driver;
> > > 72 struct klist_node knode_bus;
> > > 73 void *driver_data;
> > > 74 struct device *device;
> > > 75 };
> >
> > From device_add():
> >
> > if (parent)
> > klist_add_tail(&dev->p->knode_parent,
> > &parent->p->klist_children);
>
> that's a parent -> child relationship. What we have on this case is:
>
> -------------- ---------------
> | | | | |\
> | UHH | clocks, etc | USBTLL | | |
> | | <==========> | | <======> | | <====> ports
> | ------- | | (Transceiver- | | |
> | | EHCI | | | less Link) | |/
> | ------- | | | Port MUX
> | | | |
> | ------- | | |
> | | OHCI | | | |
> | ------- | | |
> | | | |
> -------------- ---------------
>
> It doesn't shown here, but the TLL link is completely optional. It's
> mainly used for modem integration, IIRC. Still, if we're using TLL, EHCI
> and OHCI will depend on a clock provided by the USBTLL block.
>
> Clearly, USBTLL isn't either a parent of UHH, nor a parent of EHCI/OHCI
> blocks. We can, from a code perspective, make USBTLL into a parent of
> UHH to make things simpler, but this will mean that calling
> pm_runtime_get() will also unconditionaly turn on TLL clock, unless we
> add some nasty hacks to allow TLL know if *HCI port is in TLL mode.
>
> That's why I decided for making TLL and UHH siblings, because that's a
> closer relationship than parent-child.
>
> Can you see the problem now ?
Okay, now I understand better. The word "sibling" implies that the two
objects have the same parent, so a different word would describe this
relationship better. Something like "friend" or "associate".
Or maybe, following Paul's suggestion, the driver core doesn't have to
be changed at all.
Alan Stern
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