On Jul 8, 2012, at 9:59 PM, Arnaud Lacombe wrote:
> 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...
There's no way to support overlapping IVAR keys, yes. However, if you are
designing the ivars for multiple inheritance, then you'll need to make them
non-overlapping. Thankfully, this is trivial to do.
Warner
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