linux-kernel - Re: [RFC PATCH 00/16] Refine PCI host bridge scan interfaces

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Date:	Thu, 20 Nov 2014 12:54:48 +0100
From:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>, linux-arm-kernel@...ts.infradead.org
CC:	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>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Suravee.Suthikulpanit@....com,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Yijing Wang <wangyijing@...wei.com>,
	linux-ia64@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Wuyun <wuyun.wu@...wei.com>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH 00/16] Refine PCI host bridge scan interfaces

On 17.11.2014 15:13, Arnd Bergmann wrote:
> On Monday 17 November 2014 18:21:34 Yijing Wang wrote:
>> This series is based Linux 3.18-rc1 and Lorenzo Pieralisi's
>> arm PCI domain cleanup patches, link:
>> https://patchwork.ozlabs.org/patch/407585/
>>
>> Current pci scan interfaces like pci_scan_root_bus() and directly
>> call pci_create_root_bus()/pci_scan_child_bus() lack flexiblity.
>> Some platform infos like PCI domain and msi_chip have to be
>> associated to PCI bus by some arch specific function.
>> We want to make a generic pci_host_bridge, and make it hold
>> the platform infos or hook. Then we could eliminate the lots
>> of arch pci_domain_nr, also we could associate some platform
>> ops something like pci_get_msi_chip(struct pci_dev *dev)
>> with pci_host_bridge to avoid introduce arch weak functions.
>>
>> This RFC version not for all platforms, just applied the new
>> scan interface in x86/arm/powerpc/ia64, I will refresh other
>> platforms after the core pci scan interfaces are ok.
>
> I think overall this is a good direction to take, in particular
> moving more things into struct pci_host_bridge so we can
> slim down the architecture specific code.
>
> I don't particularly like the way you use the 'pci_host_info'
> to pass callback pointers and some of the generic information.
> This duplicates some of the issues we are currently trying
> to untangle in the arm32 code to make drivers easier to share
> between architectures.
>
> As a general approach, I'd rather see generic helper functions
> being exported by the PCI core that a driver may or may not
> call.
> The way you split the interface between things that happen
> before scanning the buses (pci_create_host_bridge) and
> the actual scanning (__pci_create_root_bus, pci_scan_child_bus)
> seems very helpful and I think we can expand that concept further:
>
> - The normal pci_create_host_bridge() function can contain
>    all of the DT scanning functions (finding bus/mem/io resources,
>    finding the msi-parent), while drivers that don't depend on DT
>    for this information can call the same function and fill the
>    same things after they have the pci_host_bridge pointer.

How about finding PCI domain number (in the DT way) within 
pci_create_host_bridge() too ?

Tomasz
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