linux-kernel - Re: SNB PCI root information

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Date:	Tue, 19 Jun 2012 06:36:20 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ulrich Drepper <drepper@...il.com>, jbarnes@...tuousgeek.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	lenb@...nel.org, x86@...nel.org, linux-pci@...r.kernel.org
Subject: Re: SNB PCI root information

On Mon, Jun 18, 2012 at 5:40 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Mon, Jun 18, 2012 at 3:30 PM, Ulrich Drepper <drepper@...il.com> wrote:
>> On Sat, Jun 16, 2012 at 5:56 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>> If ACPI provides a perfectly usable generic way to describe this
>>> topology and the vendor BIOS doesn't bother to use it, I'm not very
>>> interested in trying to compensate for that BIOS deficiency by adding
>>> a bunch of non-portable CPU-specific gunk to Linux.
>>
>> The problem is that all machines get this wrong.  I've tested varies
>> models from Dell and HP and none of them have the _PXM entry and the
>> local_cpus fields are wrong.  If there is a reasonably sane way to
>> compensate for broken BIOSes it should be considered.  We all know how
>> good BIOS authors are...
>
> please check attached one. and  you may append "pci=busnum_node=00:00,80:01"
> to change node for root bus.
> assume you have two root bus: 00, 80

I'm not opposed to something like this, if people think it's useful.

This patch sets the node quite early, before we even look at the _PXM
information in pci_acpi_scan_root().  That means if the BIOS does
supply a _PXM method and the user gives this argument, the
user-supplied info is silently overwritten.  To me it would make more
sense to handle an option like this *after* we look for _PXM info.
That way it could be used to compensate for both missing and incorrect
_PXM info.
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