linux-kernel - Re: [PATCH 6/6] x86/PCI: quirk Thunderbolt PCI-to-PCI bridges

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Date:	Thu, 27 Jun 2013 10:27:59 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Penner, Miles J" <miles.j.penner@...el.com>,
	Bruce Allan <bruce.w.allan@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 6/6] x86/PCI: quirk Thunderbolt PCI-to-PCI bridges

On Thu, Jun 27, 2013 at 9:00 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Wed, Jun 26, 2013 at 5:56 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> On Wed, Jun 26, 2013 at 3:55 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>> On Wed, Jun 26, 2013 at 4:31 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>>> On Wed, Jun 26, 2013 at 3:26 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>>>> On Wed, Jun 26, 2013 at 3:18 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>>>>> On Tue, Jun 25, 2013 at 10:22 AM, Mika Westerberg
>>>>>> <mika.westerberg@...ux.intel.com> wrote:
>>>>>>> Thunderbolt PCI-to-PCI bridges typically use BIOS "assisted" enumeration.
>>>>>>> This means that the BIOS will allocate bridge resources based on some
>>>>>>> assumptions of a maximum Thunderbolt chain. It also disables native PCIe
>>>>>>> hotplug of the root port where the Thunderbolt host router is connected.
>>>> ...
>>>> During acpi hotplug, firmare could do extra help for us like assign
>>>> some resources to pci device bars, so it is NOT "boot-time".
>>>
>>> Really?  How can firmware assign BARs at hotplug-time?  I mean,
>>> obviously firmware *can* write things to the BARs before giving the
>>> device to the OS, but how would it know what to write?
>>
>> should be acpi code, or SMI code or even BMC firmware via sideband.
>
> How would that code (ACPI code (by which I assume you mean AML), SMI
> code, BMC firmware) know what values to write to BARs?  Is it reading
> the windows of upstream bridges from config space?  Is it assuming the
> OS never changes the windows of bridges upstream from the Thunderbolt
> controller?

Kernel only try to change upstream bridge for pciehp during hot-add.

for acpiphp, because could have other devices already there before hot-add,
kernel does not try to expand the upstream bridge. size and assign only
to the new added devices.

>
>>>  I assume the
>>> OS owns the address space, and it can change the upstream bridge
>>> windows or the BARs of another device on the bus at any time, subject
>>> to the OS's own issues as far as quiescing or unbinding drivers, etc.,
>>> but without coordinating with the BIOS.
>>
>> for thunderbolt or dock with acpiphp, then all children devices/bridges should
>> not have drivers loaded yet.
>
> I said "upstream bridge windows or ... another device on the bus,"
> i.e., I'm referring to devices other than the Thunderbolt controller.
> I assume the OS is free to change resource assignments for those
> non-Thunderbolt devices, and obviously those assignments affect what
> is available for Thunderbolt.

ok. that upstream one can not be touched from firmware.
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