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

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Date:	Thu, 27 Jun 2013 10:00:48 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
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 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?

>>  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.

Bjorn
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