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Intel Titan Ridge controllers (and if I gather correctly, Ice Lake CPUs) are DisplayPort 1.4 and TB3 compatible (Intel Ark).

I understand very well how this works in DisplayPort Alternate Mode: the host is told to switch into this alternate mode and from that point on, the cable is basically a DisplayPort cable with a different connector. If we have a laptop with a DisplayPort 1.4 capable GPU and Titan Ridge and a 3440x1440 @ 144 Hz monitor (which requires more DP bandwidth than DP 1.2 has) I would expect every USB C dock / adapter with a DisplayPort output to just work because all the dock needs to do is blindly connect the lanes in the USB C connection carrying DisplayPort signals to the DisplayPort outputs.

I can't wrap my head around the Thunderbolt story, however. What's the compatibility expectation here? Let's take an Alpine Ridge based dock which is the majority of the market currently. Do we expect the monitor to work at full resolution and frequency if plugged into a DisplayPort port on the dock? If monitor has a USB C input but not Thunderbolt input, would plugging that into the downstream port of the dock work? My understanding is the TB3 standard requires the downstream ports to work in DP alt mode (this answer corroborates) but I do not know about the DP version here. How much does the TB3 controller dock "interpret" and how much does it slavishly copy?

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  • I do not get the close votes , there are very specific questions in there. 1) With a specific laptop, dock, monitor what happens? 2) How does the Thunderbolt bus demultiplexing work especially as related to DisplayPort versions?
    – chx
    Mar 23, 2020 at 4:52
  • I can explain the close votes: It is not clear what the question is. The title of the question does not focus on the specific scenario described in the body of the post. Potentially, this question is answered by a link to the ref-spec of DP1.4 and TB3.0 - but this is not what the author is asking for. Mar 26, 2020 at 18:44
  • PLEASE link to the ref-spec of TB3.0 if you can!!!! (Nor you can to the DisplayPort standard but that's less of a problem here.)
    – chx
    Mar 26, 2020 at 19:11

2 Answers 2

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Alpine Ridge can only output HBR2 (whether from downstream Thunderbolt port or DisplayPort).

Alpine Ridge can pass a Thunderbolt HBR3 stream from upstream Titan Ridge since it is just Thunderbolt packets. If you connect a Titan Ridge device to the Alpine Ridge downstream Thunderbolt port, then the Titan Ridge can convert the Thunderbolt DisplayPort stream to HBR3. Similarly, a Thunderbolt display that uses a Titan Ridge controller can be connected to an intermediate Alpine Ridge device and get HBR3 (of course, the upstream source of the Thunderbolt DisplayPort stream still needs to be Titan Ridge).

An Apple Pro Display XDR requires two HBR3 connections over a single Thunderbolt cable to get 6K 60Hz (the display has two tiles) when using a GPU that doesn't support DSC. Apple's drivers won't allow dual HBR3 through an intermediate Thunderbolt device - the display needs to be connected directly to the Mac or Blackmagic eGPU. Windows drivers don't allow dual HBR3 at all. I'm not sure if dual HBR3 works in Boot Camp. Normally, Titan Ridge allows HBR2+HBR2 or HBR3+HBR (neither exceeds the max Thunderbolt bandwidth of 40 Gbps) over a single Thunderbolt cable. Dual HBR3 can exceed the max Thunderbolt bandwidth but it can be allowed if the resolution doesn't require the full bandwidth of HBR3 (such as each tile of the 6K display) because Thunderbolt does not transmit DisplayPort stuffing symbols - the controller recreates the stuffing symbols when converting the Thunderbolt DisplayPort stream back into DisplayPort. DisplayPort over Thunderbolt is described in the USB4 spec (since USB4 uses the same method as Thunderbolt).

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  • So when emitting displayPort either through the DP port or the downstream port in DP alt mode, Alpine Ridge can't just pass through the HBR3 packets?
    – chx
    Mar 30, 2020 at 0:57
  • Alpine Ridge supports DisplayPort 1.2. This means it can take DisplayPort 1.2 as input or output DisplayPort 1.2.
    – joevt
    Mar 30, 2020 at 1:55
  • Converting a Thunderbolt DisplayPort stream to DisplayPort is not a passive process. Stuffing symbols need to be recreated, etc. Alpine Ridge probably can't pass HBR3 packets because it doesn't have an HBR3 option (8.1 Gbps). It only supports up to HBR2 (5.4 Gbps). DisplayPort 1.4 uses different DisplayPort registers to specify the HBR3 speed. The computer can read the register if Alpine Ridge cannot but you still have the problem above where the computer can't tell Alpine Ridge to use an HBR3 option that does not exist.
    – joevt
    Mar 30, 2020 at 2:23
  • I did some tests with Titan Ridge host and a DisplayPort 1.4 display. With Falcon Ridge (Thunderbolt 2), DPCD register 0x2201 shows HBR3 capability With Alpine Ridge (Thunderbolt 3), DPCD register 0x2201 shows HBR2 capability - maybe it means that DisplayPort 1.4 is known but is overrides? With Titan Ridge (Thunderbolt 3) connected to Alpine Ridge, DPCD register is HBR3 and I get an HBR3 connection, allowing 4K 120Hz.
    – joevt
    Mar 30, 2020 at 2:46
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Alpine Ridge controllers can support two streams of DisplayPort 1.2. The new Titan Ridge controllers are required for supporting DisplayPort 1.4.

Wikipedia Thunderbolt (interface) explains how it works:

A single Mini DisplayPort monitor or other device of any kind may be connected directly or at the very end of the chain. Thunderbolt is interoperable with DP-1.1a compatible devices. When connected to a DP-compatible device, the Thunderbolt port can provide a native DisplayPort signal with four lanes of output data at no more than 5.4 Gbit/s per Thunderbolt lane. When connected to a Thunderbolt device, the per-lane data rate becomes 10 Gbit/s and the four Thunderbolt lanes are configured as two duplex lanes, each 10 Gbit/s comprising one lane of input and one lane of output.

The speeds possible for each lane per each DisplayPort technology is summed up by an Anand Tech article in the following chart:

enter image description here

In the new Titan Ridge family, Intel introduced three new Thunderbolt 3 controllers: JHL 7340, JHL 7440 and JHL 7540, compared in the same article with the previous controller generations:

enter image description here

Starting with the JHL7440, Intel dual-port controllers are designed specifically for peripherals and are intended to enable compatibility between TB3 peripherals and USB-C hosts.

Alpine Ridge controllers only work with Thunderbolt 3 ports and cannot fall back to being USB-C sinks. However, the JHL7440 and later controllers can fall back for use as a USB-C sink, allowing "basic compatibility" with USB-C ports.

References:

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  • 1. Anandtech is not reliable 2. This answers none of my questions. I knew all this. I need much deeper knowledge than what an Anadtech article can provide. This question probably can only be answered by someone who has read the standard which is not available to the general public or else I'd have read it myself. I even left a comment just with the questions to make it crystal clear what needs answering.
    – chx
    Mar 24, 2020 at 22:20
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    1. The Anand Tech article was the most seriously in-depth article that I found and should not be discarded. 2. If you are looking for technical manuals and circuit schemata, these are not published, and may even be classified as trade secrets. If published, cheaper compatible products will surely happen pretty soon. Intel's interest is to postpone that as much as possible.
    – harrymc
    Mar 25, 2020 at 7:34
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    3. As regarding the compatibility story for DisplayPort 1.4 and Thunderbolt 3.0, I think I have covered it pretty well.
    – harrymc
    Mar 25, 2020 at 9:19
  • With a specific laptop, dock, monitor what happens? <= That was the question. Given a DP 1.4 capable host (GPU, TB3 controller) and an Alpine Ridge dock and a DP 1.3/1.4 requiring monitor, what happens if the monitor is plugged into a Displayport on the dock and what happens when plugged into the downstream TB3 port?
    – chx
    Mar 26, 2020 at 8:05
  • No general answer is possible, since the technology is relatively new. That depends on the making and compatibility of the dock, port, cable and connected device, so I suppose that each combination needs to be verified. The general rule is that Alpine Ridge can only support DP 1.2 so at best 4K@60Hz (if all device protocol negotiations and everything else works correctly).
    – harrymc
    Mar 26, 2020 at 9:09

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