Date: Sun, 8 Jul 2012 21:31:37 -0600 From: Warner Losh <imp@bsdimp.com> To: Arnaud Lacombe <lacombar@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: newbus' ivar's limitation.. Message-ID: <5C18109D-E7A8-4868-BEA9-26B63360BB24@bsdimp.com> In-Reply-To: <CACqU3MVy65ck%2Bb8TKXwfXnBV9iuFzj%2ButRBH4Ecg6XDz3Vg5kQ@mail.gmail.com> References: <CACqU3MVh6shncm2Vtqj9oe_HxowWscCZ1eJf0q2F%2B=t_xKKBfQ@mail.gmail.com> <31A0DCE7-3B93-41BC-805A-E0B163892112@bsdimp.com> <CACqU3MVy65ck%2Bb8TKXwfXnBV9iuFzj%2ButRBH4Ecg6XDz3Vg5kQ@mail.gmail.com>
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On Jul 8, 2012, at 9:26 PM, Arnaud Lacombe wrote:
> Hi,
>=20
> On Sun, Jul 8, 2012 at 10:07 PM, Warner Losh <imp@bsdimp.com> wrote:
>>=20
>> 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.
>>=20
>> 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.
>>=20
>> So I'm not sure I understand what you are saying here.
>>=20
> dev0 implements two interfaces: A and B. dev1, child of dev0, needs to
> 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 =
values. If the Ivar keys don't overlap, then there's no problems at =
all. Certainly less hackish than not using them at all. Since dev0 =
knows the layout 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 those from B in the right part. Apart from the =
coordination of Ivar numbers, as I outlined in my last post, there's no =
issue here.
Warner
> - Arnaud
>=20
>> 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,
>> ....
>> };
>>=20
>> 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:
>>=20
>> enum ivar_namespace {
>> IVAR_PCI =3D 1,
>> IVAR_PCCARD,
>> IVAR_USB,
>> etc
>> };
>> #define IVAR_SHIFT 16
>>=20
>> and the above could be changed to:
>>=20
>> enum pci_device_ivars {
>> PCI_IVAR_SUBVENDOR =3D IVAR_PCI << IVAR_SHIFT,
>> PCI_IVAR_SUBDEVICE,
>> PCI_IVAR_VENDOR,
>> ....
>> };
>>=20
>> and then we'd have an unambiguous key, and the bus could easily =
implement multiple interfaces.
>>=20
>> but then again, most of the existing interfaces in the kernel are =
mutually exclusive, so you could implement this just for your new =
interfaces.
>>=20
>>> 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.
>>=20
>> 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.
>>=20
>>> 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....
>>=20
>> 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.
>>=20
>> Warner
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