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

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Message-ID: <CAE9FiQXcFC-5VKGVDZc6Tb8Nw8cLG4sB=BEP-+zctf2c6n6oNg@mail.gmail.com>
Date:	Wed, 9 May 2012 22:42:06 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Richard Yang <weiyang@...ux.vnet.ibm.com>
Cc:	Wei Yang <weiyang.kernel@...il.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: One problem in reassign pci bus number?

On Wed, May 9, 2012 at 8:35 PM, Richard Yang <weiyang@...ux.vnet.ibm.com> wrote:
> On Mon, May 07, 2012 at 08:42:59PM -0700, Yinghai Lu wrote:
>>>>no, probe_resource will get from start if space is big enough.
>>>>
>>>>if not, it will try to extend top.
>>>
>>> Hmm... for example we still have this
>>>               parent[70-160]
>>> brother1[70-80]  res[90-150]  brother2[151-160]
>>>                   ->child[105-140]
>>>
>>> if we call probe_resource(res, new_res, 16, par, 1, 0xff,
>>> IORESOURCE_PCI_FIXED);
>>>
>>> I think this call is used to allocate a res of size 16 under res.
>>> When there is no enough free space, it will expend res, and res->parent.
>>>
>>> While in this situation, res doesn't have enough free space. so it need
>>> to expend itself.
>>>
>>> In the probe_resource() it tries to extend res on the right side.
>>> So even there is enough space between brother1 and res, I think the
>>> probe_resource() will not return 0.
>>>
>>> Do you think my analysis is correct?
>>
>>it will reduce needed size one by one. so at last it will return
>>[91, 104]
> Yes, agree. This is the current behavior.
>
> While in this case.
>                70-160]
>  brother1[70-80]  res[90-150]  brother151-160]
>                    ->child
>
> There is free space between 81-89, and 90-104. These two free range add
> up to 25, which is more than the required space, 16.
>
> If we have this resource tree.
>           parent[70-180]
>  brother1[70-80]  re[90-150]  brothr2[170-180]
>                  d[105-140]
>
> There are enough free space between res and brother2.
> Then probe_resource will return [141-156] with size 16.
> And also expend res.
>
> So I mean this is the design decision to not count in the free space on
> the left? Even there is enough free space?

We can not extend start.

when we have bridge using [90, 150] all children devices will be on bus 90.
if change the bridge to use low like 81, then all device need to
remove and rescan them.

also keep the old bus number is safer.

Yinghai
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