linux-kernel - Re: [PATCH] PCI: Detect and trust built-in TBT chips

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Message-ID: <CA+Y6NJHeYwikO4UFzHcchjyF6qws2zaFXnsPLMO_NKp_MEXvxw@mail.gmail.com>
Date: Wed, 7 Aug 2024 17:17:22 -0400
From: Esther Shimanovich <eshimanovich@...omium.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Rajat Jain <rajatja@...gle.com>, 
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Lukas Wunner <lukas@...ner.de>, 
	Mika Westerberg <mika.westerberg@...ux.intel.com>, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Detect and trust built-in TBT chips

On Tue, Aug 6, 2024 at 6:04 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> So is this fundamentally a firmware defect?  ACPI says a Root Port is
> an "ExternalFacingPort", but the Root Port is actually connected to an
> internal Thunderbolt chip, not an external connector?
>
This seems to be a case of neglecting to add another ACPI definition
that distinguishes internal Thunderbolt chips from user-removable
ones.
ExternalFacingPort is not 100% accurate all of the time, as we just
discovered, but it does clearly describe what root port we are talking
about.

>
> I need more context to be convinced that this is a reliable heuristic.
> What keeps somebody from plugging a discrete Thunderbolt/USB4
> controller into an external port?  Maybe this just needs a sentence or
> two from Lukas's (?) helpful intro to tunneling?

Can you point me to this resource?

Thanks for your suggestions and requests for clarification! I'll
incorporate them into the next patch.