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 19:44:36 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Arnd Bergmann <arnd@...db.de>
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 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.

> 
>>>> +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.


> 
>>>> +	host = kzalloc(sizeof(*host), GFP_KERNEL);
>>>> +	if (!host)
>>>> +		return NULL;
>>>
>>> devm_kzalloc maybe?
>>
>> I don't know much detail about devm_kzalloc(), but we have no pci host driver
>> here, and I found no devm_kzalloc() uses in core PCI code before.
> 
> It also depends on having a valid device pointer. The idea is that the memory
> is automatically freed if the probe() function returns with an error, or
> the device driver gets unloaded. For the classic PCI hosts that are not
> connected to a device, that wouldn't work of course.
> 
> 	Arnd
> 
> .
> 


-- 
Thanks!
Yijing

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