linux-kernel - Re: One problem in reassign pci bus number?

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Date:	Sun, 13 May 2012 22:40:41 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Richard Yang <weiyang@...ux.vnet.ibm.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: One problem in reassign pci bus number?

On Sun, May 13, 2012 at 6:55 PM, Richard Yang
<weiyang@...ux.vnet.ibm.com> wrote:
> On Mon, Apr 23, 2012 at 03:46:03PM -0400, Don Dutile wrote:
>>On 04/22/2012 11:52 AM, Richard Yang wrote:
>>>All,
>>>
>>>I am reading the pci_scan_bridge() and not sure what will happen in
>>>following situation.
>>>
>>>Suppose the kernel is not passed the pci=assign-busses.
>>>
>>>Below is a picture about the pci system.
>>>
>>>                    +-------+
>>>                    |       | root bridge(0,255)
>>>                    +---+---+
>>>                        |          Bus 0
>>>       -----+-----------+------------------------------+--
>>>            |                                          |
>>>            |                                          |
>>>            |                                          |
>>>       +----+----+                               +-----+-----+
>>>       |         |  B1(1,15)                     |           |B2(16,28)
>>>       +----+----+                               +-----+-----+
>>>            |  Bus 1                                   |    Bus 16
>>>       -----+-----------------------         ----------+----------------
>>>                             |
>>>                        +----+----+
>>>                        |         | B3
>>>                        +---------+
>>>
>>>Suppose B1 and B2 works fine with the BIOS, which get the right bus
>>>number and range.
>>>
>>>B3 does not works fine with the BIOS, which doesn't get the bus number.
>>>
>>>So in pci_scan_bridge(), B3 will be met in the second pass and get bus
>>>number 16?
>>
> Yinghai,
>
> Take my original question.
>
> B3 doesn't get the bus number, which its parent doesn't have free bus
> number and there is no gap between B1 and B2.
>
> So in this case, the probe_resource() can't find bus number for B3.
> Then cause pci_bridge_probe_busn_res() return non-zero.
>
> Then B3 couldn't work fine?

B3 is on Bus 1? B3 is the one of bridges on Bus1?

if B3 is only bridge on Bus1, it probe_resource should return [2,15]
at first, and then scan B3.

Yinghai
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