linux-kernel - Re: [PATCH v3 00/22] PCI: Iterate pci host bridge instead of pci root bus

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Date:	Wed, 6 Feb 2013 10:59:11 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Jiang Liu <jiang.liu@...wei.com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Toshi Kani <toshi.kani@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pci@...r.kernel.org, Russell King <linux@....linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 00/22] PCI: Iterate pci host bridge instead of pci root bus

On Wed, Feb 6, 2013 at 9:54 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> I think you're missing the point.
>
> Search the tree for uses of "for_each_pci_dev()."  Almost every
> occurrence is a bug because that code doesn't work correctly for
> hot-added devices.  That code gets run for devices that are present at
> boot, but not for devices hot-added later.
>
> You're proposing to add "for_each_pci_host_bridge()."  That will have
> the exact same problem as for_each_pci_dev() already does.  Code that
> uses it will work for host bridges present at boot, but not for
> bridges hot-added later.
>
> Why would we want to add an interface when every use of that interface
> will be a design bug?  I think we should fix the existing users of
> pci_root_buses by changing their designs so they will work correctly
> with host bridge hotplug.

I'm a little confused about what you want.

In boot stage using for_each_pci_host_bridge or pci_root_buses is fine.

For those cases that it should support host-bridge by nature.
there are two solutions:
1. use for_each_pci_host_bridge, and it is hotplug-safe.
and make sgi_hotplug to use acpi_pci_driver interface.
and acpi_pci_root_add() will call .add in the acpi_pci_driver.

2. make them all to be built-in, and  those acpi_pci_driver should be registered
much early before acpi_pci_root_add is called.
then we don't need to call for_each_host_bridge for it.

So difference between them:
1. still keep the module support, and register acpi_pci_driver later.
2. built-in support only, and need to register acpi_pci_driver early.

Please let me which one you like.

Thanks

Yinghai
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