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?
32 Answers
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).
4Alpine Ridge controllers can support two streams of DisplayPort 1.2. The new Titan Ridge controllers are required for supporting DisplayPort 1.4.
WikipediaThunderbolt (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 Techarticlein the following chart:
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:
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:
7
