linux-kernel - Re: [PATCH v6 03/30] PCI: Export busn

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Message-ID: <55024405.8040504@huawei.com>
Date:	Fri, 13 Mar 2015 09:57:25 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Jiang Liu <jiang.liu@...ux.intel.com>, <linux-pci@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	<linux-kernel@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>, <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tony Luck <tony.luck@...el.com>, <linux-ia64@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	"Guan Xuetao" <gxt@...c.pku.edu.cn>, <linux-alpha@...r.kernel.org>,
	<linux-m68k@...ts.linux-m68k.org>, Liviu Dudau <liviu@...au.co.uk>,
	"Arnd Bergmann" <arnd@...db.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v6 03/30] PCI: Export busn_resource to drivers/pci

>> Hi Bjorn, busn_resource may would not be shared by multi domains,
>>
>> We insert bus number resource like:
>>
>> pci_add_resource(&resources, &busn_resource);	
>> 	pci_bus_insert_busn_res(root_bus, start, bus_max);	//start is the root bus number provided by arch pci host driver, bus max here == 255
>> 		get_pci_domain_busn_res(domain)	//for root bus	//try to get a domain specific pci_domain_busn_res, if not exist, create it.
>> 			request_resource_conflict(domain_specific_busn_res, res)   //request busn res(start, bus_max) from the pci_domain_busn_res.
>>
>> So every domain has its own pci_domain_busn_res , different domain would not share the same bus number resource.
> 
> The intent of pci_add_resource() and passing the resulting resource list
> into pci_scan_root_bus(), etc., is that the host bridge may consume any
> resources described by the list.  If we pass the same resource to multiple
> calls, that means the resource must be shared between the multiple host
> bridges involved.  For bus numbers, that makes some sense if the platform
> considers the bridges to be in the same domain, but not if they are in
> different domains.
> 
> If we export busn_resource, we have no control over what domains it becomes
> associated with because the domain is passed into pci_scan_root_bus() by
> the caller.

Agree, I will drop this patch, thanks!

> 
> Bjorn
> 
> .
> 


-- 
Thanks!
Yijing

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