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

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Message-ID: <4AE5545E.1020900@jp.fujitsu.com>
Date:	Mon, 26 Oct 2009 16:48:46 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.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 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)?

>> - 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.

Thanks,
Kenji Kaneshige

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