Re: [PATCH] thunderbolt: Add support for INTEL_FALCON_RIDGE_2C controller

[Xavier Gnata <xavier.gnata@gmail.com>]

> On Wed, Jul 13, 2016 at 12:17:33AM +0200, Andreas Noever wrote:
>> Are thunderbolt controllers always installed directly below the root
>> port? In theory there could be more bridges in between (a candidate
>> for such a topology would be the mac pro which has 3 controllers).
>
> Hm, good point. I failed to find lspci or dmesg output for a MacPro6,1
> but I did find this diagram:
> http://i.imgur.com/ItIqxDY.png
>
> Turns out the 3 controllers are connected to a PCIe switch.
> And according to the PCIe spec, a switch consists of an upstream
> bridge and downstream bridges. So the parent of the Thunderbolt
> upstream port would be a downstream port and not a root port. :-/
>
>
> Another idea would be to detect if the parent of the Thunderbolt
> upstream port has the VSEC 0x1234. This is only present on Thunderbolt
> devices, so a host controller is identifiable by the non-presence of
> that VSEC on its parent. Patch [01/13] of my runpm series adds a
> convenient is_thunderbolt flag to detect the VSEC:
> https://github.com/l1k/linux/commit/8148c395ef6e
>
> Generally I think it would be beneficial to replace the PCI quirk
> with code that lives in drivers/thunderbolt/. Here's an example what
> I have in mind, this is based on top of the runpm series and ensures
> that the NHI resumes before the hotplug ports by waking it directly
> from the upstream bridge:
> https://github.com/l1k/linux/commit/c596932608cd
>
> An even better approach would probably be Rafael's "device links"
> series which allows the PM core to take care of device dependencies
> beyond the mere parent/child relationship:
> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1170039.html
>
> Best regards,
>
> Lukas
>
I agree that it would be a good idea to get rid of both the subsystem 
vendor/device id and the quirk.
I quite like the approach of 
https://github.com/l1k/linux/commit/c596932608cd : Do you want me to 
give it a try on my hardware?
Rafael's approach is more ambitious and complex but even cleaner.
Maybe a two step approach : First we get rid of the quirk and we support 
INTEL_FALCON_RIDGE_2C controller and, in a longer run, we try to 
implement these functional dependencies in PCI core.
Anyway you are the experts :)


Xavier