On Jul 8, 2012, at 7:22 PM, Arnaud Lacombe wrote:
> Ok, yet another Newbus' limitation. Assuming a device exports more
> than one interface, and one of its child has need to use more than one
> interface, each interfaces cannot register, concurrently, its own
> ivar. While I try to always have a single child per
> interface/resource, I need to keep some compatibility with the old way
> of doing thing (POLA wrt. drivers I cannot/will not convert and
> userland). So, it would have been nice if ivar had been per-interface,
> not global and unique to one device.
There's one pointer for the ivars. The bus code gets to determine what the
ivar looks like, because the interface is totally private to the bus. So long
as it returns the right thing for any key that's presented, it doesn't matter
quite how things are done.
So I'm not sure I understand what you are saying here.
The problem, more basically, is that the ivar keys are not unique. Currently,
there's no bits used in the key to define the values to be non-overlapping.
For example:
enum pci_device_ivars {
PCI_IVAR_SUBVENDOR,
PCI_IVAR_SUBDEVICE,
PCI_IVAR_VENDOR,
....
};
We could easily reserve the upper 16-bits of this field to be that key. This
value could then be used to differentiate them. But this wouldn't scale too
well. Given that there's only about a dozen or two in the tree, that's right
at the moment, it wouldn't be hard to do something like:
enum ivar_namespace {
IVAR_PCI = 1,
IVAR_PCCARD,
IVAR_USB,
etc
};
#define IVAR_SHIFT 16
and the above could be changed to:
enum pci_device_ivars {
PCI_IVAR_SUBVENDOR = IVAR_PCI << IVAR_SHIFT,
PCI_IVAR_SUBDEVICE,
PCI_IVAR_VENDOR,
....
};
and then we'd have an unambiguous key, and the bus could easily implement
multiple interfaces.
but then again, most of the existing interfaces in the kernel are mutually
exclusive, so you could implement this just for your new interfaces.
> Unless I am mistaken, ivar are the only way for a parent can transmit
> information to a child. I can not simply implement a new METHOD to get
> that ivar as the device implements multiple time the same function
> (actually, up to 4 time for one, 3 for the other, with possible
> crossovers...), each one physically distinct. Each child is being tied
> to a pair. Thus, I need to pass each child discriminator(s) for each
> interfaces right after having been *created*, which cannot be done
> later on. Of course, it is out-of-question to have crossover in the
> interfaces definitions.
ivars are but one way to communicate this. However, they are the generic way
to convert a key to a value and store a key on a value. I don't really
understand what you are trying to say here, perhaps an example would help
illustrate what you are trying to do, since I don't quite understand the
problem here.
> The best way I could achieve this currently is to pass the child's
> device to its parent, and do a lookup based on that pointer to get
> information I need, but erk....
That doesn't make any sense. The child's parent already sets that child's ivar
when the child is created. The child's parent already gets a pointer to the
child when asked to do the key to value translation. Again, perhaps an example
would help here.
Warner_______________________________________________
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