Re: [Linux-ia64] translating ACPI _HID & _UID to PCI bus number

[Mike Smith <msmith@freebsd.org>]

It's not actually clear from the conversation so far what exactly Matt is 
after.  I get the impression, however, that what he wants to do is 
synthesise an _HID/_UID pair, which is not quite what's being discussed 
here.

If that's the case, typically _HID is the 32-bit vendor/device ID of the 
controller, and _UID is the instance count for the given _HID, eg. the 
first controller has a _UID of 0, the second has a _UID of 1, etc.

> In general a PCI device does not need to have _HID or _UID, because _ADR is
> used for that purpose. If a PCI device happens to be on a root PCI bus, it
> has _HID and _UID as well. So the bus number is avaialble from _BBN on the
> bus, assuming that the OS does not change the PCI bus number.

This isn't entirely correct either.

> -----Original Message-----
> From: Lee, Jung-Ik 
> Sent: Wednesday, May 02, 2001 2:02 PM
> To: Nakajima, Jun; 'Matt_Domsch@Dell.com';
> acpi@phobos.fachschaften.tu-muenchen.de
> Cc: linux-ia64@linuxia64.org
> Subject: RE: [Linux-ia64] translating ACPI _HID & _UID to PCI bus number
> 
> 
> Even with ACPI namespace, {_HID, _UID} pair does not tell the path of a
> device in a given topology, and can not produce a PCI bus number(vice
> versa).
> _ADR of PCI device does not provide bus number either. It's just dev +func.
>
> So to get PCI bus number of a given PCI bus:
> 1. you can use _BBN of the device, but this works only on root pci bridges.
> I personally want to see all PCI bridges have _BBN method for OSPM's
> convenience, but ACPI spec does not require it for non-roots.

This is because ACPI assumes that you have a functional bus architecture. 
The created bus instance should know its bus number, either from _BBN or 
from querying the bridge's secondary bus number register, so as a device 
you just query your parent for its bus number.

Because Matt's tool is running in userspace, however, this may not be so 
easy to achieve.

> Thus, there seems to be no perfect solutions here... to get pci bus number
> from acpi name space alone.

That's basically correct; you can't do this.

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