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From: John Baldwin <jhb@freebsd.org>
To: "Grover, Andrew" <andrew.grover@intel.com>
Cc: "acpi-jp@jp.FreeBSD.org" <acpi-jp@jp.FreeBSD.org>
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Date: Fri, 20 Sep 2002 14:44:55 -0400
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Subject: [acpi-jp 1839] RE: ACPI Question
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On 20-Sep-2002 Grover, Andrew wrote:
> (I figured I'd just respond to your original mail :)
> 
>> From: John Baldwin [mailto:jhb@freebsd.org] 
>> Ok, I have a question.  Do all Host-PCI bridges have to be enumerated
>> by ACPI?
> 
> Yes.

Great!  Thanks.

>>  From my reading of the ACPI 2.0a spec, I'm not sure.  I know
>> that ACPI doesn't have to enumerate devices that can be found through
>> other standard means unless it is overriding standard behavior.
>> However, it also says that all Host-PCI bridges need a _PRT.  Hence
>> my confusion.  If anyone could enlighten me I would appreciate it.
> 
> Host-PCI bridges cannot be enumerated today, without making the assumption
> that there is a bus 0. I don't know about FBSD but Linux, pre-ACPI, both
> assumes a PCI bus 0, and does a "peer bus trick" to find other peer root
> bridges.

Yes, we do the same.

> With ACPI, this assumption is no longer necessary, because pci root bridges
> are explicitly enumerated, and _BBN gives the base bus number if it is not
> 0.
> 
> I'm not clear on how _PRT relates to this...

I was under the impression that futzing around on PCI bus 0 looking for
host bridges was an accepted way of doing things and thus that ACPI might
not be required to enumerate them.

I already have patches that I will commit for i386 that create a small
legacy(4) driver that the old APM drivers and the old host-PCI bridge
driver will hang off.  We will only use the legacy(4) driver if we don't
find ACPI and it is enabled.  This prevents host-PCI bridges from being
probed twice, etc.

Thanks again.

-- 

John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/
