Re: USB type-C altmode support for UCSI

[Mika Westerberg]

On Wed, Sep 05, 2018 at 04:24:29PM +0300, Heikki Krogerus wrote:
> +Mika, Mario, LKML
> 
> On Mon, Sep 03, 2018 at 02:17:46PM +0000, whitequark wrote:
> > After looking through LKML, I've seen that people refer to you when
> > discussing issues with USB-C device compatibility. Do you think you
> > could help me with an Apple Thunderbolt 2 to 3 adapter? I've spent
> > quite a while studying USB-C, reverse engineering platform and
> > adapter firmware and so on, and I'm quite stumped.
> > 
> > I have a Dell XPS13 laptop. UCSI advertises port altmodes
> > 8087:00000001, ff01:00001c46, 413c:00000001, in that order.
> > When I plug in the adapter, UCSI advertises partner altmode
> > 8087:00000001. A billboard class device enumerates. Nothing else
> > happens; the Thunderbolt NHI device doesn't appear, and if I force
> > it to appear via the WMI hook, there are no Thunderbolt events,
> > and the only device on the Thunderbolt bus is the root switch.

Some Dell XPS systems do not support that TBT2<->TBT3 adapter. I think I
tried this on XPS 15 9550 and XPS 13 9365 and in both cases it is
rejected. I think it has something to do with the PD controller
firmware. Same goes if you Plug TB16 dock and to that dock then connect
the adapter + device.

Mario probably has more input about this one.