Messages in this thread | | | Subject | Re: USB type-C altmode support for UCSI | Date | Fri, 07 Sep 2018 11:04:27 +0000 | From | whitequark <> |
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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
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