Re: Thunderbolt: One missing DisplayPort?

[Stefan Hoffmeister <stefan.hoffmeister@gmail.com>]

On Mon, May 30, 2022 at 10:33 AM Tomasz Moń <desowin@gmail.com> wrote:
>
> On Sun, 2022-05-29 at 21:51 +0200, Stefan Hoffmeister wrote:
> > I have managed to wedge the system into a state where it does not
> > know about Thunderbolt, and now, on what I presume to be USB-C only

> Could you please tell how did you wedge the system into a state where
> it does not know about Thunderbolt?

I was thinking of going the "find a bad-enough good cable" route as
mentioned by Mika, but then I discovered that I possess only
* a Thunderbolt cable
* a 100W power delivery cable (which to my surprise still does what
appears to be USB 2.0)
and that it was the weekend.

Incidentally I had been poking at the "Dell Client Configuration
Toolkit" (hardly advertised) previously - which, at least in its
RedHat 8 incarnation, will destroy anything related to openssl (in
particular sudoers) through ldconfig on Fedora 36 in a native
installation, with much fun ensuing given a disabled root account. But
I digress.

The "Dell Client Configuration Toolkit" gives you command-line access
to the BIOS on modern (2018+) Dell boxes; this exposes a BIOS
configuration option (not visible / recognizable in the BIOS UI) to
set "ThunderboltPorts" to "Disabled". Setting that to "Enabled" didn't
make the laptop explode, so "Disabled" apparently reconfigured /
forced the onboard TB4 Intel controller to forget everything about
Thunderbolt, ending up with plain USB-C at revision 1.2 (pretty old).

Net observable effect: "only the first screen works on Thunderbolt" we go to
* Windows 11 can do "2.5K@60 Hz + 4K @ 30 Hz", and
* Linux can do a slightly _flakey_"2.5K + 4K @ 60 Hz".

I like a stable 60 Hz screen refresh rate (enabled by native
Thunderbolt bandwidth)