linux-kernel - Re: [PATCH 01/28] PCI: Rip out pci_bus_add_devices() from pci_scan

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Date:	Mon, 19 Jan 2015 14:59:44 +1000
From:	Greg Ungerer <gregungerer@...tnet.com.au>
To:	Yijing Wang <wangyijing@...wei.com>,
	Yinghai Lu <yinghai@...nel.org>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	the arch/x86 maintainers <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>,
	"linux-ia64@...r.kernel.org" <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>,
	"sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>
Subject: Re: [PATCH 01/28] PCI: Rip out pci_bus_add_devices() from pci_scan_bus()

On 19/01/15 12:04, Yijing Wang wrote:
> On 2015/1/17 7:16, Yinghai Lu wrote:
>> On Fri, Jan 16, 2015 at 3:15 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>> On Thu, Jan 15, 2015 at 5:43 PM, Yijing Wang <wangyijing@...wei.com> wrote:
>>>> Pci_bus_add_devices() should not be placed in pci_scan_bus().
>>>> Now pci device will be added to driver core once its
>>>> creation. All things left in pci_bus_add_devices() are
>>>> driver attachment and other trivial sysfs things.
>>>> Pci_scan_bus() should be the function responsible for
>>>> scanning PCI devices, not including driver attachment.
>>>> Other, some callers(m68k,unicore32,alpha) of pci_scan_bus()
>>>> will call pci_bus_size_bridges() and pci_bus_assign_resources()
>>>> after pci_scan_bus().
>>>>
>>>> E.g.
>>>> In m68k
>>>> mcf_pci_init()
>>>>         pci_scan_bus()
>>>>                 ...
>>>>                 pci_bus_add_devices() --- try to attach driver
>>>>         pci_fixup_irqs()
>>>>         pci_bus_size_bridges()
>>>>         pci_bus_assign_resources()
>>>>
>>>> It is not correct, resources should be assigned correctly
>>>> before attaching driver.
>>>
>> No, for booting path, at that time pci drivers are *NOT* loaded yet.
> 
> Hi Yinghai, I knew code flow here would not cause problems, sorry the log
> confused you, I will refresh it. But I think pci_scan_bus()/pci_scan_root_bus()
> which could only be used during system boot up(before module_init) make
> the pci scan logic obscure. Because most callers additionally call
> pci_bus_size_bridges() and pci_bus_assign_resources() later,
> so rip out pci_bus_add_devices() from pci_scan_bus()/pci_scan_root_bus()
> make code have better readability.

I agree that ordering seems odd. I recall there was a reason I had
to put it in that order (at that time - which is a few years back now).
I can't remember exactly now, but it was something like bridges
didn't get resourced properly without a pci scan first.

Regards
Greg



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