Re: [PATCH 0/3] Introduce Thunderbolt/USB4 <-> USB Type-C port mapping

Heikki Krogerus
2025-04-15T09:32:16Z

Hi Greg,

On Mon, Apr 14, 2025 at 09:03:42PM +0200, Greg KH wrote:
> On Mon, Apr 14, 2025 at 07:55:51PM +0200, Alan Borzeszkowski wrote:
> > Hello everyone,
> >
> > This patch series introduces the creation of symlinks between
> > Thunderbolt/USB4 ports and their corresponding USB Type-C ports. The
> > primary goal is to provide users with clear visibility into which USB4
> > port is connected via a specific Type-C port. This provides the same
> > functionality that is already present in Chromebooks.
>
> "mapping" in what way? sysfs links? If so, care to add
> Documentation/ABI/ updates?

It is already there:
https://docs.kernel.org/admin-guide/abi-testing.html#abi-sys-bus-thunderbolt-devices-usb4-portx-connector

The link is already created on Cromebooks like Alan explained, because
there each USB4/TBT port has a device node in the ACPI tables with the
appropriate _PLD (Physical Location of Device), but on systems
targeted primarily for Windows, that is not the case. There ports do
not have device nodes, so we can't make the link based on _PLD.

This series makes that same link by taking advantage of the
"usb4-host-interface" _DSD device property [1] that we always have on
those Windows platforms. That same device property that we also use in
drivers/usb/code/usb-acpi.c, and probable some other places too.

[1] https://www.usb.org/sites/default/files/D1T2-2%20-%20USB4%20on%20Windows.pdf

thanks,

--
heikki