linux-kernel - Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

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Date: Thu, 25 Apr 2024 17:16:24 -0400
From: Esther Shimanovich <eshimanovich@...omium.org>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: Mario Limonciello <mario.limonciello@....com>, Dmitry Torokhov <dmitry.torokhov@...il.com>, 
	Lukas Wunner <lukas@...ner.de>, Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Rajat Jain <rajatja@...gle.com>
Subject: Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

Thank you for all your help!

On Tue, Apr 23, 2024 at 1:33 AM Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
>
> The other way I think is something like this:
>
>   - If it does not have "usb4-host-interface" property (or behind a port
>     that has that). These are all tunneled (e.g virtual).
>
>   - It is directly connected to a PCIe root port with
>     "ExternalFacingPort" and it has sibling device that is "Thunderbolt
>     NHI". This is because you can only have "NHI" on a host router
>     according to the USB4 spec.
>
I did find one example of a docking station that uses the DSL6540
chip, which has PCI IDs defined in include/linux/pci_ids.h:
#define PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_NHI     0x1577
#define PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_BRIDGE  0x1578
It seems like it has an NHI, despite being in an external, removable
docking station. This appears to contradict what you say about only
having "NHI" on a host router. I am assuming that by host router, you
mean the fixed discrete, fixed thunderbolt chip, or the thunderbolt
controller upstream to the root port. Please correct me if I got
anything wrong!

Looking at 18-241_ThunderboltController_Brief_HI.pdf, it seems like
these Alpine Ridge chips can be used either on a computer or a
peripheral. (Expected usage: Computer or peripheral)
So I'm not sure if finding an NHI would guarantee that the device is
not a peripheral. My original question was how to distinguish a
Thunderbolt controller that is on a removable peripheral, like a
docking station-- from one that is a discrete chip fixed to a computer
or upstream to the root port.

So unless I am misunderstanding something, it appears that my only
option is waiting for Lukas's patches. Please correct me if that is
not the case!