Hi,
On Sun, Jul 8, 2012 at 10:07 PM, Warner Losh <i...@bsdimp.com> wrote:
>
> 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.
>
ok, I think I got it now. You and I are exactly saying the same thing,
just in different terms; there is no way to currently specify multiple
independent (/overlapping) ivars in a child...
- Arnaud
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