linux-kernel - Re: [Patch v5 4/6] PCI/ACPI: Consolidate common PCI host bridge code into ACPI core

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Message-ID: <20150729205417.GD9640@google.com>
Date:	Wed, 29 Jul 2015 15:54:17 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Yijing Wang <wangyijing@...wei.com>,
	Len Brown <lenb@...nel.org>, Lv Zheng <lv.zheng@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"x86 @ kernel . org" <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Patch v5 4/6] PCI/ACPI: Consolidate common PCI host bridge code
 into ACPI core

On Wed, Jun 10, 2015 at 12:58:15AM +0800, Jiang Liu wrote:
> On 2015/6/10 0:12, Lorenzo Pieralisi wrote:
> > On Mon, Jun 08, 2015 at 05:20:46PM +0100, Jiang Liu wrote:

> >> +struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
> >> +				     struct acpi_pci_root_ops *ops,
> >> +				     struct acpi_pci_root_info *info,
> >> +				     void *sysdata, int segment, int node)
> > 
> > I do not think you need to pass segment and node, they clutter the
> > function signature when you can retrieve them from root, I would
> > make them local variables and use root->segment and acpi_get_node
> > in the function body to retrieve them.
> On x86, node and segment may be overridden under certain conditions.
> For example, segment will always be 0 if 'pci_ignore_seg' is set.

I agree we should drop the segment and node parameters.  Having the
information in two places means we can make a mistake, and we can easily
avoid that possibility by only keeping it in one place.

I think it is a bug that we don't set root->segment to zero when we have
pci_ignore_seg.  Sorry, that's my fault from 1f09b09b4de0 ("x86/PCI: Ignore
_SEG on HP xw9300").

I don't understand the issue about overriding the node number.  Can you
explain it?
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