linux-kernel - Re: [PATCH 5/8] PCI: add generic device into pci_host

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Date:	Mon, 27 Feb 2012 15:24:11 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] PCI: add generic device into pci_host_bridge struct

On Mon, Feb 27, 2012 at 1:49 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Mon, Feb 27, 2012 at 11:17 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> On Mon, Feb 27, 2012 at 12:08 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>
>>>> This doesn't feel right to me.  You're allocating a new struct device
>>>> here, but the arch likely already has one.  In fact, I think we even
>>>> passed it in to pci_create_root_bus().
>>>
>>> no.
>>>
>>> original pci_create_root_bus() will create one dummy struct device and
>>> use it as parent for bus->dev.
>>>
>>>>
>>>> On x86, we already have an ACPI device for the host bridge, and now
>>>> we'll have a second one.  (Actually a *third* one, because PNPACPI
>>>> also has one, but that's a long-standing problem.)
>>>
>>> not related.
>>
>> OK.  Can you educate me?  What is the device we pass in, what does the
>> dummy one correspond to, why do we have two, what's the difference,
>> etc., etc.?
>
> for every bus will have ->bridge, and that is device pointer. to  pci
> bridge dev.
>
> for root bus, there is not pci bridge for that. So create_root_bus
> allocate local dummy one.
>
> that dummy device will be bus->dev's parent.
>
> Now pci_host_bridge is added, and it is allocated, so just put the
> struct device into that pci_host_bridge.
>
> and use pci_host_bridge->dev as parent of root bus->dev's parent.

What's the device passed in to pci_create_root_bus()?  Why is that
different than the root bus dev's parent?
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