Re: newbus' ivar's limitation..

Hi,

On Mon, Jul 9, 2012 at 1:17 AM, Arnaud Lacombe <lacombar@gmail.com> wrote:
> Hi,
>
> On Mon, Jul 9, 2012 at 12:37 AM, Warner Losh <imp@bsdimp.com> wrote:
>>
>> On Jul 8, 2012, at 9:46 PM, Arnaud Lacombe wrote:
>>
>>> On Sun, Jul 8, 2012 at 11:31 PM, Warner Losh <imp@bsdimp.com> wrote:
>>>>
>>>> On Jul 8, 2012, at 9:26 PM, Arnaud Lacombe wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> On Sun, Jul 8, 2012 at 10:07 PM, Warner Losh <imp@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-interfa=
ce,
>>>>>>> not global and unique to one device.
>>>>>>
>>>>>> There's one pointer for the ivars.  The bus code gets to determine w=
hat the ivar looks like, because the interface is totally private to the bu=
s.  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.
>>>>>>
>>>>> dev0 implements two interfaces: A and B. dev1, child of dev0, needs t=
o
>>>>> use both interfaces. There is no generic way for dev0 to export
>>>>> independent ivars for both interface. For now, I restricted the
>>>>> function of the second interface not to need ivar, but that's kind of
>>>>> hackish.
>>>>
>>>> Only if the IVARs for interface A and interface B have overlapping val=
ues.  If the Ivar keys don't overlap, then there's no problems at all.  Cer=
tainly less hackish than not using them at all.  Since dev0 knows the layou=
t of the ivar that it set on its child, this presents no problems at all.  =
It would return the values from A from the right part of the ivar, and thos=
e from B in the right part.  Apart from the coordination of Ivar numbers, a=
s I outlined in my last post, there's no issue here.
>>>>
>>> I think we should not be talking about the same API here. I have no
>>> idea what you mean by "the key to value translation", nor "Ivar
>>> numbers". What I refer to is that device_set_ivars() /
>>> device_get_ivars() acts on a single instance variables from `struct
>>> device': `ivars'. In that case, I do not really see how to set that
>>> specific field to two distinct values for each interfaces.
>>
>> We are talking about the ivar interface.  You are just misunderstanding =
how it is used.
>>
> yes I indeed did... silly, silly me :-)
>
Actually, no. I wasn't that silly, neither was I misunderstanding
anything beside how *you* wanted it to be used, which is, I sorry to
say, unacceptable. The last thing I want is to pollute an interface
with a single-purpose, hand-crafted, bus. I was to just throw away all
that ivar stuff and go into hinted child configuration for now,
waiting for FDT... but of course, I figured out after a few hours that
hinted child attachment requires `bus_hinted_child' to be set in the
parent, as does bus_enumerate_hinted_children() / bus_generic_attach()
to explicitly pollute my code. All this stuff should be done
implicitly to support N:1 interfaces/client relationship. N
*independent* interfaces being provided by a single driver; of course,
I'm not even going back to require those interface being provided by
multiple drivers, it is already a dead end.

I am not even sure any driver in the tree provides more than one interface.=
...

For whatever reason, I am more and more thinking that this all
new-bus[0] stuff is *way* overkill, static, bloated at will, and
missing critical features; a huge PITA to use, for the intended
purpose.

/me pissed.

 - Arnaud

[0]: damn, why is it even called "newbus", this stuff is 14 years old.
It really belongs to a museum, not production code...
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