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

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Message-ID: <CAE9FiQVUcYu-KM8fBs3zO5ZnL9jxHmJSN6-Ue5-kdC-niM6=Jw@mail.gmail.com>
Date:	Tue, 15 May 2012 19:11:34 -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 Tue, May 15, 2012 at 6:18 PM, Richard Yang
<weiyang@...ux.vnet.ibm.com> wrote:
> On Tue, May 15, 2012 at 10:32:46AM -0700, Yinghai Lu 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.
> So these steps is done after boot up and user find B3 doesn't work?

yes, after os is booted up.

Yinghai
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