linux-kernel - Re: [PATCH] pci: pciehp update the slot bridge res to get big range for pcie devices

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Date:	Wed, 28 Oct 2009 12:00:54 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci\@vger.kernel.org" <linux-pci@...r.kernel.org>,
	Alex Chiang <achiang@...com>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Bjorn Helgaas <bjorn.helgaas@...com>
Subject: Re: [PATCH] pci: pciehp update the slot bridge res to get big range for pcie devices

Yinghai Lu <yinghai@...nel.org> writes:

> Kenji Kaneshige wrote:
>> Yinghai Lu wrote:
>>> Yinghai Lu wrote:
>>>> Kenji Kaneshige wrote:
>>>>> I understand you need to touch I/O base/limit and Mem base/limit. But
>>>>> I don't understand why you also need to update bridge's BARs. Could
>>>>> you please explain a little more about it?
>>>>>
>>>>> Just in case, my terminology "bridge's BARs" is Base Address Register
>>>>> 0 (offset 0x10) and Base Address Register 1 (offset 0x14) in the
>>>>> (type 1) configuration space header of the bridge.
>>>> i mean 0x1c, 0x20, 0x28
>>>>
>>>> did not notice that bridge device's 0x10, 0x14 are used...
>>>> if port service need to use 0x10, 0x14, and the device is enabled, we
>>>> should touch 0x10, and 0x14.
>>>
>>> after check the code, if
>>> pci_bridge_assign_resources ==> pdev_assign_resources_sorted ==> 
>>> pdev_sort_resources
>>>
>>> will not touch 0x10 and 0x14, if those resource is claimed by port
>>> service.
>>>
>>> /* Sort resources by alignment */
>>> void pdev_sort_resources(struct pci_dev *dev, struct resource_list *head)
>>> {               int i;
>>>                         for (i = 0; i < PCI_NUM_RESOURCES; i++) {
>>>                 struct resource *r;
>>>                 struct resource_list *list, *tmp;
>>>                 resource_size_t r_align;
>>>                                 r = &dev->resource[i];
>>>                                         if (r->flags &
>>> IORESOURCE_PCI_FIXED)
>>>                         continue;
>>>                         if (!(r->flags) || r->parent)
>>>                         continue;
>>>                
>>> r->parent != NULL, will make it skip those two.
>>>
>>> So -v3 should be safe.
>>>
>> 
>> Thank you for the clarification.
>> 
>> But I still don't understand the whole picture of your set of
>> changes. Let me ask some questions.
>> 
>> In my understanding of your set of changes, if there is a PCIe
>> switch with some hot-plug slots and all of those slots are empty,
>> I/O and Memory resources assigned by BIOS are all released at
>> the boot time. For example, suppose the following case.
>> 
>>                bridge(A)
>>                   |
>>        -----------------------
>>        |                     |
>>     bridge(B)             bridge(C)
>>        |                     |
>>      slot(1)               slot(2)
>>      (empty)               (empty)
>> 
>>   bridge(A): P2P bridge for switch upstream port
>>   bridge(B): P2P bridge for switch downstream port
>>   bridge(C): P2P bridge for switch downstream port
>> 
>> In the above example, I/O and Mem resource assigned to bridge(A),
>> bridge(B) and bridge(C) are all released at the boot time. Correct?
>> 
>> Then, when a adapter card is hot-added to slot(1), I/O and Mem
>> resources enough for enabling the hot-added adapter card is assigned
>> to bridge(A), bridge(B) and the adapter card. Correct?
>> 
>> Then, when an another adpater card is hot-added to slot(2), we
>> need to assign enough resource to bridge(C) and the new card.
>> But bridge(A) doesn't have enough resource for bridge(C) and
>> the new card. In addition, all bridge(A) and bridge(B) and the
>> adapter card on slot(1) are already working. How do you assign
>> resource to bridge(C) and the card on slot(2)?
>> 
>
> thanks, will update the patches to only handle leaf bridge, and don't touch min_size etc.

Tell me what is your expected behavior if I plug a bridge with hotplug
slots into a leaf hotplug slot?  Will you assign me enough resources so
that I can plug in additional devices?

Today I make plugging in a hotplug bridge work by having the firmware
reserve at one level and having the kernel reserve at the next level.

Windows handles the issue in theory by performing some kind of
hot-unplugging of drivers that already have assigned resources and
then replugging them.  Which allows a full renumbering of busses.
We don't have the infrastructure to do that safely today.

Eric
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