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

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Date:	Tue, 15 May 2012 10:32:46 -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 11:46 PM, Richard Yang
<weiyang@...ux.vnet.ibm.com> wrote:
> On Sun, May 13, 2012 at 10:40:41PM -0700, Yinghai Lu wrote:
>>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.
>>>>>
>>> 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?
> No,  I omit other bridges on Bus#1.
> They will occupy bus number 2-15, which is calculated by BIOS and set to
> bridge's configuration space.

with that new condition, probe_resource will return zero.

for those kind of case:
1. use echo 1 > /sys .../remove to remove devices under Bridge2.
2. use setpci to change bus register of bridge2 to move high to make
more space for bridge 1.
3. rescan bridge 1 and bridge 2.

Yinghai
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