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

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Date:	Tue, 5 Jun 2012 14:26:03 +0800
From:	Richard Yang <weiyang@...ux.vnet.ibm.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Richard Yang <weiyang@...ux.vnet.ibm.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: One problem in reassign pci bus number?

On Mon, Jun 04, 2012 at 04:36:33PM -0700, Yinghai Lu wrote:
>On Mon, Jun 4, 2012 at 6:34 AM, Richard Yang <weiyang@...ux.vnet.ibm.com> wrote:
>> On Tue, May 29, 2012 at 10:14:51AM -0700, Yinghai Lu wrote:
>>>On Tue, May 29, 2012 at 4:59 AM, Richard Yang
>>><weiyang@...ux.vnet.ibm.com> wrote:
>>>>
>>>> I think about this issue again, this behavior of kernel will bring some
>>>> unconvenience to the user.
>>>>
>>>> Do you think the kernel could handle this situation?
>>>
>>>in this extreme case, you may need user to do some comprise.
>>>
>>>We should always try to use setting from BIOS if it is sane.
>>>
>>>Yinghai
>> Yinghai
>>
>>                    +-------+
>>                    |       | root bridge(0,255)
>>                    +---+---+
>>                        |          Bus 0
>>       -----+-----------+------------------------------+--
>>            |                                          |
>>            |                                          |
>>            |                                          |
>>       +----+----+                               +-----+-----+
>>       |         |  B1(1,15)                     |           |B2(32,35)
>>       +----+----+                               +-----+-----+
>>            |  Bus 1                                   |    Bus 32
>>       -----+-----------------------             -----------
>>                             |
>>                        +----+----+
>>                        |         | B3
>>                        +---------+
>>
>> I reread the current code, v3.4, in linus tree,
>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
>> And I come up with another condition which will have a problem when
>> kernel is not given the parameter, pci=assign-busses.
>>
>> Same condition as previous:
>> -------------------------------------------------------------------------------
>> B1 and B2 works fine with the BIOS and get the bus number assigned.
>> B3 is not probed by BIOS.
>>
>> Difference between the previous example:
>> -------------------------------------------------------------------------------
>> In this case, B2 is assigned bus range (32, 35), which has a gap between
>> B1 number range (1, 15).
>>
>> When kernel meets B3 in second pass, B3 will be assigned with bus number
>> 16. Well, this time the bus number 16 doesn't overlap with bus number of
>> B2.
>>
>> But, the pci_fixup_parent_subordinate_busnr() will not work since the
>> pci=assign-buses is not passed to kernel.
>>
>> So B1's bus window is still (1,15) not (1,16).
>>
>> BTW, is this also a extrem case?
>
>that should be handled by busn_alloc branch.
>
>kernel will try to probe in [1,15] at first, and could extend B1 range
>to [1, 31] if needed.
Hmm... when do you think this branch will be merged to the mainstream?
>
>Thanks
>
>Yinghai

-- 
Richard Yang
Help you, Help me

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