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Date:	Mon, 26 Oct 2009 19:27:02 +0900
From:	Kenji Kaneshige <>
To:	Yinghai Lu <>
CC:	Jesse Barnes <>,
	"" <>,
	"" <>,
	Alex Chiang <>,
	Ivan Kokshaysky <>,
	Bjorn Helgaas <>
Subject: Re: [PATCH] pci: pciehp update the slot bridge res to get big range
 for pcie devices

Yinghai Lu wrote:
> Kenji Kaneshige wrote:
>> Yinghai Lu wrote:
>>> Kenji Kaneshige wrote:
>>>> Yinghai Lu wrote:
>>>>> move out bus_size_bridges and assign resources out of
>>>>> pciehp_add_bridge()
>>>>> and at last do them all together one time including slot bridge, to
>>>>> avoid to call
>>>>> assign resources several times, when there are several bridges under
>>>>> the slot bridge.
>>>>> need to introduce pci_bridge_assign_resources there.
>>>>> handle the case the first bridge that doesn't get pre-allocated big
>>>>> enough res from FW.
>>>>> for example pcie devices need 256M, but the bridge only get
>>>>> preallocated 2M...
>>>> Though I have not looked at the patch deeply yet (sorry), I have
>>>> some questions and concerns about this change. Please correct me
>>>> if my understanding is not correct.
>>>> - Your patch doesn't seems to have the code to free resources.
>>>>  If we need to expand the resource range, don't we need to free
>>>>  preallocated resource before allocating the new one?
>>> that is done with pci_bus_size_bridges ==> pbus_size_io/pbus_size_mem
>>> ==> find_free_bus_resource ==> release_resource.
>> I didn't noticed that find_free_bus_resource() was changed to call
>> release_resource() recently...
>> By the way, does this (release_resource() by find_bus_resource())
>> change the resource assignment by BIOS also for bridges other than
>> the ports with hotplug slot (switch upstreamport, for example)?
> yes.
> BIOS preallocate small range for the bridge, and leave the BAR for the device under that bridge uninitialized.

Does this happen at the boot time regardless of hot-plug?

>>>> - Your patch seems to update BARs for bridge itself. I think it
>>>>  would break the bridge's driver (port service driver) that if
>>>>  it controls the device's capability by using IO/Mem, though I
>>>>  don't know if such driver or capabilities exists now.
>>> port service driver will be AER and pciehotplug.
>>> it seems those driver are not use those BAR...
>>> those BAR are supposed for the devices under the pcie bridge.
>> I understand that there are only two port service drivers (AER and
>> PCIe hotplug) and both doesn't use BAR. But I still have a concern
>> that changing bridge's BARs might cause problems in the future. In
>> my understanding, what you need is expanding IO/Mem base and limit
>> of root or switch downstream ports. If so, I think we should only
>> touch IO/Mem base/limit, and should not touch bridge's BARs.
> those bridge BAR are for devices under that bridge. the port device is not supposed to use them.

Do you mean you touch only BARs of the devices under the bridge?

> if we don't touch the bridge's BAR, the hw will not forward the io for those devices under it.

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.

Kenji Kaneshige

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