linux-kernel - Re: [RFC PATCH 07/16] PCI: Separate pci_host_bridge creation out of pci_create_root

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Date:	Tue, 18 Nov 2014 13:25:32 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	linuxppc-dev@...ts.ozlabs.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Liviu Dudau <liviu@...au.co.uk>,
	Tony Luck <tony.luck@...el.com>,
	Russell King <linux@....linux.org.uk>,
	linux-pci@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Xinwei Hu <huxinwei@...wei.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Suravee.Suthikulpanit@....com, linux-ia64@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Wuyun <wuyun.wu@...wei.com>, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 07/16] PCI: Separate pci_host_bridge creation out of pci_create_root_bus()

On Tuesday 18 November 2014 19:44:36 Yijing Wang wrote:
> On 2014/11/18 17:30, Arnd Bergmann wrote:
> > On Tuesday 18 November 2014 16:32:26 Yijing Wang wrote:
> > 
> >>>> +static struct resource busn_resource = {
> >>>> +	.name	= "PCI busn",
> >>>> +	.start	= 0,
> >>>> +	.end	= 255,
> >>>> +	.flags	= IORESOURCE_BUS,
> >>>> +};
> >>>
> >>> I think it would be better to require callers to pass the bus resource
> >>> down to the function.
> >>
> >> Hmm, I think most of caller will provide the bus resource, but some others
> >> will not give any bus resource, extremely, no any resources :(. But we still
> >> need properly configure their resources for compatibility.
> > 
> > I think that is what the conversion to pci_scan_bus_parented() is about:
> > The idea is that we add the correct bus resource to callers of
> > pci_scan_bus_parented or pci_scan_bus and then change them to call
> > pci_scan_root_bus instead.
> 
> It looks good to me, but for simplification, or I will try to use a wrapper to
> process the drivers don't pass the busnr resources, and make sure the generic
> pci_create_host_bridge() always get the valid resources.

Ok.
 
> >>>> +struct pci_host_bridge *pci_create_host_bridge(
> >>>> +		struct device *parent, u32 db, 
> >>>> +		struct pci_ops *ops, void *sysdata, 
> >>>> +		struct list_head *resources)
> >>>> +{
> >>>
> >>> Do we still need to pass the 'sysdata' in here? If we are guaranteed to
> >>> have a device pointer, we should always be able to get the driver
> >>> private data from dev_get_drvdata(host->dev->parent).
> >>
> >> We need, some platforms pass NULL pointer as host bridge parent.
> > 
> > But those don't have to use the new pci_create_host_bridge() function,
> > right?
> 
> As I mentioned in another reply, I hope all pci host drivers could use
> pci_create_host_bridge(), keep different PCI scan interfaces in PCI core
> make things become complex.

Doing this for all platforms that have PCI support would be a lot of
work though, I think it's better to focus on having a the best interface
for the majority of users.

	Arnd
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