linux-kernel - Re: [PATCH v2 5/5] PCI: Remove redundant 'quirk_amd_nb

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Message-ID: <CAErSpo77c5F0vftHEOFFwvXLa7S2DZzPdTjO4v6zRGcpJmjj3w@mail.gmail.com>
Date:	Tue, 29 Apr 2014 13:29:32 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Suravee Suthikulanit <suravee.suthikulpanit@....com>
Cc:	Daniel J Blueman <daniel@...ascale.com>,
	Myron Stowe <myron.stowe@...il.com>,
	Borislav Petkov <bp@...e.de>,
	Myron Stowe <myron.stowe@...hat.com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>,
	kim.naru@....com, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86 <x86@...nel.org>,
	Steffen Persvold <sp@...ascale.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] PCI: Remove redundant 'quirk_amd_nb_node'

On Mon, Apr 28, 2014 at 8:02 PM, Suravee Suthikulanit
<suravee.suthikulpanit@....com> wrote:

> Sorry for late reply.  My concern is that removing the "quirk_amd_nb_node()"
> will affect the value of "numa_node" of the host bridge devices (i.e.
> X:00.[18|19|1a|1b|1c|1d|1e|1f].X).  I am not sure if any code is using this
> information.  But in theory, these host-bridge devices are not on the same
> node as where the PCI root complex lives (e.g. 0 and 4 from the example
> above).

I doubt anything in the kernel uses the node number for these devices
(00:[18|19|...]).  The only place the PCI core uses it is to run a
driver probe method on the same node as the device.  Are there even
drivers for these devices?

They aren't PCI-to-PCI bridges, so there are no devices below them
that would be affected by their node numbers.

> If we want the "numa_node" to really representing the actual node, then the
> quirk has to stay for now.  We might need to come up with a different logic
> to replace the quirks here, which would automatically determine the actual
> node value for these host-bridge devices.

It sounds like the numa_node for these devices in sysfs is misleading
unless we have a quirk like this.  If that's important, I think it
could be fixed by having the BIOS provide _PXM methods for them.  But
I don't think it is, and I'm inclined to remove the quirk.

I'm pushing hard to get rid of CPU-specific code like this because
there are generic methods to do it, e.g., _PXM, and the CPU-specific
code is a perennial maintenance headache.

Bjorn
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