Re: Thunderbolt: One missing DisplayPort?

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Thu, Jun 02, 2022 at 09:34:27PM +0200, Tomasz Moń wrote:
> On Mon, 2022-05-30 at 12:54 +0300, Mika Westerberg wrote:
> > On Mon, May 30, 2022 at 10:33:06AM +0200, Tomasz Moń 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
> > > > ("usb_typec_revision" == 1.2? Seems ... low?), both DisplayPort
> > > > outputs on the docking station are now active, and I do get
> > > > meaningful entries from the DRM subsystem (and hence X). I am half-
> > > > way happy: I want exactly that over Thunderbolt for the bandwidth ;)
> > > 
> > > Could you please tell how did you wedge the system into a state where
> > > it does not know about Thunderbolt?
> > > 
> > > > Now, when I unwedge the system to enable Thunderbolt again
> > > 
> > > I am curious about the wedge/unwedge procedure.
> > 
> > Probably just connecting the dock using non-Thunderbolt Type-C cable.
> > That will enter USB (+DP altmode) or so instead of Thunderbolt altmode.
> 
> How do I determine that the cable is non-Thunderbolt Type-C?

It does not have that "lightning" logo on the connector.

> I have tried with two different brands 1m USB Type-C cables that are
> not advertised as Thunderbolt. Both cables are electronically marked
> and 5A capable. When the docking station is connected using these
> cables, it operates in Thunderbolt mode.

Oh, yeah it is possible actually that with a passive type-C cable that
it still enters TBT/USB4 mode (20G). I think.

> If the device was operating in USB (+DP altmode), I assume that boltctl
> would show that the docking station status as disconnected?

Correct.

> Can I read the cable EMCA details in Linux?

This I don't know.