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

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Date:	Fri, 4 May 2012 12:52:05 +0800
From:	Richard Yang <weiyang@...ux.vnet.ibm.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Richard Yang <weiyang@...ux.vnet.ibm.com>,
	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 Thu, May 03, 2012 at 08:15:29PM -0700, Yinghai Lu wrote:
>>>
>>>I updated for-pci-busn-alloc branch with updating of probe_resource()...
>>>and removing bus->secondary and subordinate.
>>>
>> You mean you remove the bus->secondary field?
>> So the pci_bus->number hold the bus number?
>> I think this is a huge work.
>>>Please check if you can understand it ...
>>>
>>>http://git.kernel.org/?p=linux/kernel/git/yinghai/linux-yinghai.git;a=commitdiff;h=7de8df57b223d54af95ffe67f8da2dd39a265971
>> Some question:
>>
>> +static resource_size_t __find_res_top_free_size(struct resource *res,
>> +                                                int skip_nr)
>> +{
>> +       resource_size_t n_size;
>> +       struct resource tmp_res;
>> +
>> +       */
>> +        *   find out free number below res->end that we can use.
>> +        *      res->start to res->start + skip_nr - 1 can not be used.
>> +        */
>> +       n_size = resource_size(res);
>> +       if (n_size <= skip_nr)
>> +               return 0;
>> +
>> +       n_size -= skip_nr;
>> +       memset(&tmp_res, 0, sizeof(struct resource));
>> +       while (n_size > 0) {
>> +               int ret;
>> +
>> +               ret = __allocate_resource(res, &tmp_res, n_size,
>> +                       res->end - n_size + skip_nr, res->end,
>> +                       1, NULL, NULL, false);
>> +               if (ret == 0) {
>> +                       __release_resource(&tmp_res);
>> +                       break;
>> +               }
>> +               n_size--;
>> +       }
>> +
>> +       return n_size;
>> +}
>> So this is trying to find out the biggest free space of res?
>> On the right side?
>>
>> For example we have , res like
>>   90-150
>>        105-140
>> The __find_res_top_free_size() will return 10 instead of 15.
>> So this is the design decision to find the right side free resouce not
>> the left side?
>
> __find_res_top_free_size()  is called by probe_resource().
>
>probe_resource will return [91-104].
Hmm... I think the result is returned by this while loop.
+       while (n_size >= needed_size) {
+               ret = allocate_resource(b_res, busn_res, n_size,
+                               b_res->start + skip_nr, b_res->end,
+                               1, NULL, NULL);
+               if (!ret)
+                       return ret;
+               n_size--;
+       }
__find_res_top_free_size() is not called.

BTW, even if this value is returned by __find_res_top_free_size(), or
returned after this function is called, the purpose of the
__find_res_top_free_size() is to get the biggest free space under the
first parameter?
>
>Thanks
>
>Yinghai

-- 
Richard Yang
Help you, Help me

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