linux-kernel - Re: [PATCH 1/2][RESEND] x86/pci/amd: Restore early_fill_mp_bus_to

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Date:	Fri, 4 May 2012 10:35:05 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Andreas Herrmann <andreas.herrmann3@....com>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH 1/2][RESEND] x86/pci/amd: Restore early_fill_mp_bus_to_node

On Fri, May 4, 2012 at 7:03 AM, Andreas Herrmann
<andreas.herrmann3@....com> wrote:
> On Wed, May 02, 2012 at 11:33:17AM -0600, Bjorn Helgaas wrote:
>> On Fri, Apr 27, 2012 at 8:36 AM, Andreas Herrmann
>> <andreas.herrmann3@....com> wrote:
>> >
>> > Once upon a time this function was overloaded with quirky stuff to fix
>> > resource detection on systems w/ _CRS defects (seems that some Sun and
>> > HP systems were affected).
>> >
>> > See commit 30a18d6c3f1e774de656ebd8ff219d53e2ba4029
>> > (x86: multi pci root bus with different io resource range, on 64-bit)
>> >
>> > Restore the old function and thus decouple it from the quirk that is
>> > CPU family specific (e.g. it won't work on AMD family 15h CPUs). BTW,
>> > I assume that the _CRS stuff is working on current systems.
>> >
>> > This is required to properly initilize the numa_node information of
>> > existing PCI busses and associated devices.
>>
>> I applied some of Yinghai's patches that also touch this area.  Can
>> you refresh these so they apply on top of my "next" branch
>> (git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git next)?
>
> Arrgh, will adapt my patch and resend it (asap).
>
>> Can you also be more specific about what these patches fix?
>
>> My understanding is that amd_bus.c (1) sets NUMA info with
>> set_mp_bus_to_node() and (2) figures out MMIO and I/O port apertures,
>> which are only used when blind probing and when ignoring _CRS.
>>
>> It seems like the main change in this patch is that we skip (2)
>> completely when family >= 0x11, and I don't understand what that could
>> fix.
>
> The patch restores a very old function that was used to detect the
> nearest node for a PCI bus, so yes it's used to do (1). IMHO this
> function was totally screwed up with Yinghai's code to do (2). It
> seems that Sun has (had?) some systems where (2) was req'd. I don't
> care about this part. But I'd like to do (1) on all AMD CPU NUMA
> systems.

Thanks for the explanation.  But I'm afraid I'm still confused.

First, it sounds like you're trying to change the way we do part (1),
i.e., the set_mp_bus_to_node() calls, but I think the effect of your
patch is to stop doing part (2) in some cases.

Second, I am pretty sure that the current early_fill_mp_bus_info()
(before your patch) does the exact same set_mp_bus_to_node() calls as
your early_fill_mp_bus_to_node() does.

Finally, on all systems with ACPI, the set_mp_bus_to_node() call in
pci_acpi_scan_root() should be doing what you need.  In fact, that
call happens later, so it should be overwriting the information filled
in by amd_bus.c.  If there's something wrong in this ACPI path, the
most likely cause is a BIOS defect, such as  a missing _PXM method on
the PNP0A03/0A08 host bridge device.

Bjorn
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