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Dock which can support thunderbolt4 and hdmi 2.1?
Hi all. For my work I use Dell. Privately I use a new macbook pro with thunderbolt 4. I'm looking at buying a LG OLED 4k@120Hz screen. I currently use a Dell WD19 dock. So I need to upgrade my dock. Is there a Dell dock and a converter which would enable me to send 4k@120Hz through the dock to a hdmi 2.1 tv? As far as I can tell the only potential solution would be to get the performance dock and then use thunderbolt 3 both upstream and downstream and get a usb-c --> HDMI 2.1 converter. Would this even work? I've been unable to find a dock that can handle this guaranteed. Everything seems to be that you can buy it, cross your fingers and hope for the best.
Thank you for your help!
jphughan
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November 16th, 2021 06:00
@Melmix USB-C to HDMI 2.1 adapters can enable 4K 120 Hz output if the source USB-C port supports DisplayPort 1.4/HBR3. In a dock scenario, that would require both the dock and attached system to support that standard. Video traffic over USB-C and Thunderbolt is DisplayPort natively.
If your “new MacBook Pro” is the 2021 model with an M1 Pro or M1 Max chip, it supports that standard. Although fyi just for the benefit of people who might read threads like these well into the future, it’s helpful to specify an exact model rather than saying “new” at the time you post. Similarly, it doesn’t matter in this specific case, but in many cases the size of the MBP is an important bit of information since at least in the past, the hardware specs of 13” vs. 15” systems was different in crucial ways.
In terms of your work system, I have no idea whether it supports that standard because the system model wasn’t specified.
But the Dell WD19TBS is a Thunderbolt dock with USB-C ports that support DisplayPort 1.4/HBR3 output. It can also provide up to 90W of power to non-Dell systems. So while I don’t have the equipment to test this myself, the specs and underlying technologies suggest that a USB-C to HDMI 2.1 adapter should allow you to get 4K 120 Hz out of a WD19TBS’s USB-C port when you’re running it from a 2021 MBP. However, a potential stumbling block is that the WD19TBS specifically might force Macs to run in DP 1.2/HBR2 mode. This has to do with how GPU interfaces work over Thunderbolt and how the WD19TBS allocates video bandwidth across its ports, both of which vary depending on the DisplayPort revision in use, as well as the fact that macOS still doesn’t support DisplayPort MST, which creates some problem scenarios when trying to run multiple displays through Thunderbolt when using DP 1.4/HBR3. If that is the case and affects the new 2021 MBP — neither of which I am completely certain about — then 4K 120 Hz through a WD19TBS from a Mac likely won’t be possible, and the reason would be that Dell is essentially working around an annoying limitation of macOS and chose to do so in a way that prioritizes multiple display support over single high-bandwidth display support.
Also note that even if this does work, you may be unable to run any OTHER display through the dock simultaneously, simply due to the amount of bandwidth 4K 120 Hz consumes.
But in terms of finding a dock with an integrated HDMI 2.1 port, that may take a while to arrive, for two reasons. The first is that the main use case for that today is 4K 120 Hz, and high refresh rate displays still aren’t all that common, and are even less common in work settings where docks are most often used. The second reason is that HDMI 2.1 supports up to 48 Gbps of bandwidth, which is more than Thunderbolt 3 and 4 even BEFORE considering that Thunderbolt has to carry both video and PCIe traffic. So HDMI 2.1 would be bottlenecked by Thunderbolt and thus prevented from being fully utilized, which could create confusion and aggravation for users who did not realize this and found themselves unable to use an HDMI 2.1 port on a Thunderbolt dock to its maximum capacity. But HDMI 2.1 adapters still have value today in enabling 4K 120 Hz.
Worst case of course you could just connect the USB-C to HDMI 2.1 adapter directly to a USB-C port on your MBP. And depending on your work laptop model, that may be an option there too. I realize it’s an additional cable, but that would also remove the requirement to spend money upgrading the dock.
Melmix
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November 16th, 2021 10:00
Thank you. It's a MacBook Pro 2021 max model with 10 core CPU, 32 core gpu, 32gb mem and 1tb storage.
The Dell laptop is a latitude 7400.
It looks like the new m1 pro and max support mst
https://appleinsider.com/articles/21/10/18/new-m1-pro-m1-max-macbook-pros-support-more-displays-than-m1-macs
jphughan
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November 16th, 2021 15:00
@Melmix The Latitude 7400 is a DisplayPort 1.2/HBR2 system, so it wouldn't be able to run 4K 120 Hz. As for MST, the ability to support more displays is not MST. DisplayPort MST is the ability to run multiple displays from a single GPU interface. macOS still does not support that, which I know because I have a 2021 MBP here myself and when I connect it to my daisy chain of dual 1440p displays, I get mirrored output rather than the system realizing there are two independent displays on the daisy chain as all of my PC laptops do. This matters because Thunderbolt can carry up to two DisplayPort interfaces. When used with a Mac that doesn't support MST, that means you can only run two displays from that Thunderbolt dock, whereas a PC might be able to run three or four as long as the bandwidth requirements of the displays didn't exceed what was available. But the reason HBR2 vs HBR3 comes into play is that with HBR2, Thunderbolt carries two full HBR2 interfaces. With HBR3, which offers more bandwidth per interface, Thunderbolt carries one interface plus 25% of a second interface. This means that when you're working with a Mac where displays cannot share an interface as allowed by MST, you might not be able to run two of the same types of displays, unless you're running displays that each require no more than 25% of an HBR3 interface, since that will be the lowest common denominator.from a bandwidth standpoint.
Melmix
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November 16th, 2021 19:00
My understanding is that this was only an issue on the earlier M1 and is resolved on the M1 Pro / Max. I may be wrong. Unfortunately you write a mbp 2021 without specifying which model.
jphughan
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November 16th, 2021 22:00
@Melmix I have a 14” MBP with an M1 Pro. I have seen zero indication that these systems support DisplayPort MST. The article you linked didn’t address that at all. And thus far, lack of MST support has been a limitation of macOS, not a hardware limitation. This became clear with Intel-based Macs that could not run MST while running macOS, but could run MST just fine when booted into Windows via Boot Camp. The difference between the M1 and the M1 Pro/Max is the total number of displays that they can run. The M1 could only run two (including the built-in display on the MacBooks as opposed to the Mac Mini), while the M1 Pro can run three and the M1 Max can run five. But the total number of displays you can run is completely separate from the ability to run multiple displays from a single GPU interface. That is what DisplayPort MST allows. And that is why Windows systems that support MST can run 2-3 displays from a regular USB-C dock even though it only taps into a single GPU interface, whereas Macs can only run a single display through that type of dock. And on Thunderbolt, PCs can run 3-4 displays even though Thunderbolt can only carry two GPU interfaces over a single Thunderbolt connection, whereas Macs can only run two displays through a single Thunderbolt connection.
If you believe you’ve found some information that contradicts what I’ve just said, I’d appreciate you sharing it, but lack of MST support has been a point of complaint from Mac users for YEARS on this forum, Apple’s forum, and elsewhere on the Internet, because it’s existed on the PC side for about a decade now. And I follow this type of laptop tech pretty closely.