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

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Date:	Tue, 18 Nov 2014 11:45:18 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Yijing Wang <wangyijing@...wei.com>,
	Liviu Dudau <liviu@...au.co.uk>,
	Tony Luck <tony.luck@...el.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"huxinwei@...wei.com" <huxinwei@...wei.com>,
	Thierry Reding <thierry.reding@...il.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wuyun <wuyun.wu@...wei.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 00/16] Refine PCI host bridge scan interfaces

On Tue, Nov 18, 2014 at 11:30:11AM +0000, Arnd Bergmann wrote:
> On Tuesday 18 November 2014 19:17:32 Yijing Wang wrote:
> > On 2014/11/17 22:13, 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.
> > 
> > Hi Arnd, thanks very much for your review and comments!
> > 
> > > 
> > > 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.
> > 
> > What arm32 code you are trying to untangle for example ?
> 
> We have a few problems that currently prevent us from using shared
> drivers across arm32 and arm64:
> 
> - arm32 has an architecture-defined pci_sys_data structure, but
>   we really want to have one that is defined by the host bridge driver
>   and that is architecture independent. Some core functions depend
>   on this structure at the moment, which Lorenzo is trying to
>   undo

Yes, and on this specific point I would like to understand why we
are adding yet more pci_sys_data data in the last series that is
already in -next:

https://lkml.org/lkml/2014/10/27/85

What does this buy us ? The cover letter says already that there *is*
a better solution, why do not we work on that instead of adding more churn
to arch specific code ?

Thanks,
Lorenzo
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