Re: USB type-C altmode support for UCSI

[whitequark <whitequark@whitequark.org>]

On 2018-09-05 14:13, whitequark wrote:
> On 2018-09-05 13:50, Mario.Limonciello@dell.com wrote:
>> 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.
> 
> This is my understanding as well, however I'd like to fix this issue.
> From looking at the BIOS image I can see that the 9360 uses a TPS65982
> USB PD controller. The adapter uses a TPS65983A (confusingly remarked
> by Apple as CD3215B). I've seen reports on the web that there is some
> inherent incompatibility between TPS65982 and TPS65983, however TI is
> for some reason extremely secretive about TPS65983 and I wasn't able
> to get anything definitive about it.
> 
> Anyway, I've reverse engineered a nontrivial part of the TI TPS6598x
> firmware and register layout, however my understanding of Thunderbolt
> and USB PD is not sufficient to proceed.
> 
> Mario, do you think you could get in touch with the people at Dell who
> work with USB PD and ask if:
> 
>   (a) the adapter advertising an altmode with SVID:0x8087 
> VDO:0x00010001
>       is the problem here, and
>   (b) whether configuring the register 0x52 Intel VID Configuration in
>       the adapter's USB PD controller to set TBTModeDataTXSOP=0x0000
>       would help.

I have been able to verify two things by reflashing the adapter with 
upstream
(non-Apple) firmware and experimenting with the configuration:

(a) the altmode with SVID:0x8087 VDO:0x00010001 (16th bit set) means 
that
     this is an altmode advertised by a legacy Thunderbolt (3 to 2) 
adapter.
     So the adapter is fine here.

(b) the Dell USB PD controller doesn't try to negotiate the altmode even 
with
     advertised VDO:0x00000001. Something else is missing in the 
configuration.

-- 
whitequark