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Apple Silicon M4 Pro Thunderbolt 5 controllers are still limited to two DisplayPort inputs each?
Kensington says their dock can support two 6K displays on an M3 Pro and two 8K on the M4 Pro. As far as I know every 5K and 6K screen is a tiled display that uses multiple DisplayPort streams per monitor(Apple’s XDR 6K uses two streams). I think the 2-monitor limit isn’t hit by DisplayPort streams, but by something else… but everything is murky.

I ordered the OWC hub and have an LG 5K and a Samsung S9 5K… I’ll see what happens.
 
Kensington says their dock can support two 6K displays on an M3 Pro and two 8K on the M4 Pro. As far as I know every 5K and 6K screen is a tiled display that uses multiple DisplayPort streams per monitor(Apple’s XDR 6K uses two streams). I think the 2-monitor limit isn’t hit by DisplayPort streams, but by something else… but everything is murky.
The newer 5K displays (Apple, Asus) and all 6K displays (Apple, Dell) may have a tiled mode but it's only used when connected to computers that don't support the single tiled mode which uses DSC.

For example, The Apple 6K display when connected using DSC requires less bandwidth than a 4K60 display that doesn't use DSC.

In Apple Silicon Macs, a dual tile display counts as 1 display but still requires two DisplayPort connections.

The original M1 Macs could connect 1 display via Thunderbolt, including dual tile displays - which means they support two DisplayPort connections but the second can only be used for the second connection of a dual tile display.

I think the ioreg command will show how many DisplayPort inputs (for hosts) and outputs (for peripherals) each Thunderbolt controller has.
Thunderbolt DP In and Out Adapters may have ioreg properties that show some DisplayPort info when a display is connected (capabilities, link rate, lane count, bandwidth).
Would be interesting to see if M4 Pro and M4 Max show a different number.

The BetterDisplay command line might indicate if a display mode is tiled or not? I haven't tried it.
https://forums.macrumors.com/thread...n-m1-m2-m3-now-possible.2381664/post-33527884
I know that info (display modes, tiled or not) exists in the ioreg.
 
Looked through ioreg and pulled out some stuff:
  1. The AppleThunderboltDPInAdapterOS2 for the 3 TB5 ports. Two AppleThunderboltDPInAdapterOS2 indicate that they have two DisplayPort connections available, which is expected.
  2. The DisplayPort@0 / DisplayPort@1 for the two 5K monitors connected. I'm guessing the one with only is the DisplayPort@0 newer Samsung 5K monitor.
So I guess the Samsung might be only using one connection... but super unsure how this works especially with MST modes.


| | | | | +-o IOThunderboltPort@5 <class IOThunderboltPort, id 0x10000093b, registered, matched, active, busy 0 (4 ms), retain 23>
| | | | | | +-o AppleThunderboltDPInAdapterOS2 <class AppleThunderboltDPInAdapterOS2, id 0x10000094c, registered, matched, active, busy 0 (3 ms), retain 9>
| | | | | +-o IOThunderboltPort@6 <class IOThunderboltPort, id 0x10000093c, registered, matched, active, busy 0 (4 ms), retain 11>
| | | | | +-o AppleThunderboltDPInAdapterOS2 <class AppleThunderboltDPInAdapterOS2, id 0x100000945, registered, matched, active, busy 0 (3 ms), retain 8>


| | | | | +-o IOThunderboltPort@5 <class IOThunderboltPort, id 0x10000084c, registered, matched, active, busy 0 (8 ms), retain 11>
| | | | | | +-o AppleThunderboltDPInAdapterOS2 <class AppleThunderboltDPInAdapterOS2, id 0x100000856, registered, matched, active, busy 0 (3 ms), retain 8>
| | | | | +-o IOThunderboltPort@6 <class IOThunderboltPort, id 0x10000084d, registered, matched, active, busy 0 (9 ms), retain 11>
| | | | | +-o AppleThunderboltDPInAdapterOS2 <class AppleThunderboltDPInAdapterOS2, id 0x10000085f, registered, matched, active, busy 0 (5 ms), retain 8>


| | | | | +-o IOThunderboltPort@5 <class IOThunderboltPort, id 0x100000889, registered, matched, active, busy 0 (8 ms), retain 23>
| | | | | | +-o AppleThunderboltDPInAdapterOS2 <class AppleThunderboltDPInAdapterOS2, id 0x1000008b4, registered, matched, active, busy 0 (1 ms), retain 9>
| | | | | +-o IOThunderboltPort@6 <class IOThunderboltPort, id 0x10000088a, registered, matched, active, busy 0 (6 ms), retain 23>
| | | | | +-o AppleThunderboltDPInAdapterOS2 <class AppleThunderboltDPInAdapterOS2, id 0x100000896, registered, matched, active, busy 0 (2 ms), retain 9>


| | | | | +-o CIO <class IOPortTransportStateCIO, id 0x100083873, registered, matched, active, busy 0 (1913 ms), retain 15>
| | | | | +-o USB3@0 <class IOPortTransportStateUSB3, id 0x100083894, registered, matched, active, busy 0 (2 ms), retain 12>
| | | | | +-o DisplayPort@0 <class IOPortTransportStateDisplayPort, id 0x10008ca41, registered, matched, active, busy 0 (5 ms), retain 11>


| | | | +-o CIO <class IOPortTransportStateCIO, id 0x100000ad7, registered, matched, active, busy 0 (1477 ms), retain 16>
| | | | +-o DisplayPort@1 <class IOPortTransportStateDisplayPort, id 0x100001827, registered, matched, active, busy 0 (331 ms), retain 11>
| | | | +-o DisplayPort@0 <class IOPortTransportStateDisplayPort, id 0x1000894ee, registered, matched, active, busy 0 (6 ms), retain 11>
 
Looked through ioreg and pulled out some stuff:
  1. The AppleThunderboltDPInAdapterOS2 for the 3 TB5 ports. Two AppleThunderboltDPInAdapterOS2 indicate that they have two DisplayPort connections available, which is expected.
  2. The DisplayPort@0 / DisplayPort@1 for the two 5K monitors connected. I'm guessing the one with only is the DisplayPort@0 newer Samsung 5K monitor.
So I guess the Samsung might be only using one connection... but super unsure how this works especially with MST modes.
Hmm. You don't see any DPOut ?
Try the following command. It dumps all the items but not any properties except those that contain ' DP '. It dumps the class inheritance so we can see how these DPIn adapters related to older DPIn adapters or other types of adapters. It removes the non class info (id, flags, busy, retain count) which are not informative.
ioreg -fliw0 | sed -nE 's/, id .*/>/;/\+\-o/p;/ DP /p' > ioreg_dp.txt
You can zip the results and attach to your post.

MST is used for old 4K displays that are dual tile displays. For 5K and 6K, dual tile modes use dual SST (if DSC isn't).
MST is multiple streams over a single DisplayPort connection.
SST is a single stream over a DisplayPort connection.
dual SST is two DisplayPort connections.

You can try the BetterDisplay command line to list all the display modes. Does it show any tiled modes?
You can use one of my scripts:
This one is slow: https://gist.github.com/joevt/0c75b42171b3fb1a5248b4e2bee8e4d0
This one is faster: https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8

If you have an Intel Mac, then this one might be interesting. It will get the DPCD of the display. And the EDID. And any display related info in ioreg.
https://github.com/joevt/AllRez
 
Hmm. You don't see any DPOut ?
Try the following command. It dumps all the items but not any properties except those that contain ' DP '. It dumps the class inheritance so we can see how these DPIn adapters related to older DPIn adapters or other types of adapters. It removes the non class info (id, flags, busy, retain count) which are not informative.
ioreg -fliw0 | sed -nE 's/, id .*/>/;/\+\-o/p;/ DP /p' > ioreg_dp.txt
You can zip the results and attach to your post.

MST is used for old 4K displays that are dual tile displays. For 5K and 6K, dual tile modes use dual SST (if DSC isn't).
MST is multiple streams over a single DisplayPort connection.
SST is a single stream over a DisplayPort connection.
dual SST is two DisplayPort connections.

You can try the BetterDisplay command line to list all the display modes. Does it show any tiled modes?
You can use one of my scripts:
This one is slow: https://gist.github.com/joevt/0c75b42171b3fb1a5248b4e2bee8e4d0
This one is faster: https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8

If you have an Intel Mac, then this one might be interesting. It will get the DPCD of the display. And the EDID. And any display related info in ioreg.
https://github.com/joevt/AllRez

BetterDisplay doesn't show anything about "tile"/"tiling" in the exported report for either of my 5K displays(S27C900P or LG UltraFine).

It appears both screens have two AppleThunderboltDPOutAdapter in ioreg.

Code:
    | |   | |     |   |     +-o IOThunderboltPort@D  <class IOThunderboltPort, id 0x10008387a, registered, matched, active, busy 0 (90 ms), retain 22>
    | |   | |     |   |     | +-o AppleThunderboltDPOutAdapterOS  <class AppleThunderboltDPOutAdapterOS, id 0x100083883, registered, matched, active, busy 0 (4 ms), retain 9>
    | |   | |     |   |     +-o IOThunderboltPort@E  <class IOThunderboltPort, id 0x10008387b, registered, matched, active, busy 0 (92 ms), retain 11>
    | |   | |     |   |     | +-o AppleThunderboltDPOutAdapterOS  <class AppleThunderboltDPOutAdapterOS, id 0x100083884, registered, matched, active, busy 0 (7 ms), retain 9>

...

    | |   | |     |   |     +-o IOThunderboltPort@8  <class IOThunderboltPort, id 0x100001737, registered, matched, active, busy 0 (225 ms), retain 23>
    | |   | |     |   |     | +-o AppleThunderboltDPOutAdapterCM  <class AppleThunderboltDPOutAdapterCM, id 0x10000173b, registered, matched, active, busy 0 (1 ms), retain 10>
    | |   | |     |   |     +-o IOThunderboltPort@B  <class IOThunderboltPort, id 0x100001738, registered, matched, active, busy 0 (225 ms), retain 23>
    | |   | |     |   |       +-o AppleThunderboltDPOutAdapterCM  <class AppleThunderboltDPOutAdapterCM, id 0x100001743, registered, matched, active, busy 0 (1 ms), retain 10>
 
....


I think you'll get TB5 speed at the ports on the dock, but you will be limited to TB4 data bandwidth from the host. This is not useful, unless you consider replacing the Thunderbolt 5 hub with something like a Thunderbolt 5 version of the Blackmagic eGPU or Sonnet eGPU Breakaway Puck RX 5500 XT/5700 which could use the extra bandwidth for DisplayPort data from the eGPU (except Apple Silicon Macs don't support eGPUs and PCs don't like this kind of eGPU and Apple might not update Intel macOS for Thunderbolt 5 hubs/docks/eGPUs?).
It would be useful for me if it worked.

I have a Highpoint RAID card, which is hardware raid, and lives in a PCI slot. It's speed would be bottlenecked by its connection to the Mac. I wrote to them and they said "At this time, HighPoint does not have any product that supports ThunderBolt 5. Your feedback is being reviewed internally." Since they have supported Macs extremely well, I would have thought its a perfect product for those not buying M powered Mac Pros. In other words, from T-5 Studios (if they ever arrive) and right now, the Pro Macbooks and the Pro Mac Mini.

But from looking at a user review, it seems to me that getting over 3,000 MB/s for large data flows - where the cache on the external OWC drive was fooling for a few seconds the Blackmagic speed tests - then I may as well settle for thunderbolt 3. If thunderbolt 5 is not quick at the moment, then IMO its a waste of money, I may as well buy thunderbolt 3 drives or USB 4 drives.
 
I have a new M4 Pro MacBook pro, and dual LG 5K displays. Right now, I'm plugging each display into the MacBook.

Plugging in two thunderbolt 5 cables is not a big deal, but I am having problems with sleep / wake : all my windows on my second monitor are moved back to the first monitor.

I wonder, I had this new OWC thunderbolt 5 hub, could I plug in a single cable and have both 5K displays working normally? Also, I wonder if having both monitors on the same cable could possibly help with the wake issue?
 
I wonder, I had this new OWC thunderbolt 5 hub, could I plug in a single cable and have both 5K displays working normally?
A Thunderbolt 5 dock can only support 3 DisplayPort connections.
PCs can source 3 DisplayPort connections per Thunderbolt 5 controller.
Macs can only source 2 DisplayPort connections per Thunderbolt 3/4/5 port so they can't use the full capabilities of a Thunderbolt 5 dock.
An LG UltraFine 5K display requires 2 DisplayPort connections over Thunderbolt 3/4/5 to support 5K60. The later model LG UltraFIne 5K can connect via USB-C at 4K60 (or 5K39 with a custom timing).

For PCs, only one LG UltraFine 5K can work at 5K60 from a Thunderbolt 5 dock. The other might work at 4K60 (or 5K39 with a custom timing).
For Macs, only one LG UltraFine 5K can work at 5K60 from a Thunderbolt 3/4/5 dock unless you can force both displays to use 4K60 or 5K39 with a USB-C cable instead of a Thunderbolt cable.
 
IT WORKS!

Got my OWC hub today and it works to connect both of my 5K screens(very old LG and new Samsung) on both my M4-Pro-Mini AND my M1-Max-Macbook-Pro via a single port.

I still have no idea what command would actually show info on if things are tiled or using DSC, but a single `system_profiler SPDisplaysDataType` shows the resolutions and refresh rates haven't changed when running them both through the new hub.

Code:
% system_profiler SPDisplaysDataType                                          
Graphics/Displays:


    Apple M4 Pro:


      Chipset Model: Apple M4 Pro
      Type: GPU
      Bus: Built-In
      Total Number of Cores: 16
      Vendor: Apple (0x106b)
      Metal Support: Metal 3
      Displays:
        S27C900P:
          Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
          UI Looks like: 2560 x 1440 @ 60.00Hz
          Main Display: Yes
          Mirror: Off
          Online: Yes
          Rotation: Supported
        LG UltraFine:
          Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
          UI Looks like: 2560 x 1440 @ 60.00Hz
          Mirror: Off
          Online: Yes
          Rotation: Supported
          Automatically Adjust Brightness: No
 
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IT WORKS!

Got my OWC hub today and it works to connect both of my 5K screens(very old LG and new Samsung) on both my M4-Pro-Mini AND my M1-Max-Macbook-Pro via a single port.

I still have no idea what command would actually show info on if things are tiled or using DSC, but a single `system_profiler SPDisplaysDataType` shows the resolutions and refresh rates haven't changed when running them both through the new hub.

Code:
% system_profiler SPDisplaysDataType                                         
Graphics/Displays:


    Apple M4 Pro:


      Chipset Model: Apple M4 Pro
      Type: GPU
      Bus: Built-In
      Total Number of Cores: 16
      Vendor: Apple (0x106b)
      Metal Support: Metal 3
      Displays:
        S27C900P:
          Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
          UI Looks like: 2560 x 1440 @ 60.00Hz
          Main Display: Yes
          Mirror: Off
          Online: Yes
          Rotation: Supported
        LG UltraFine:
          Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
          UI Looks like: 2560 x 1440 @ 60.00Hz
          Mirror: Off
          Online: Yes
          Rotation: Supported
          Automatically Adjust Brightness: No
If that's an LG UltraFine 5K then it is definitely not working at 5K because an Apple Silicon Mac only supports two DisplayPort connections per Thunderbolt port (even for Thunderbolt 5) and the LG UltraFine 5K requires two DisplayPort connections for 5K60 and one of those is taken by the Samsung S27C900P. You could try a custom timing of 5K39 for the LG UltraFine 5K. Try to see the difference between 5K scaled down to 4K output and 5K unscaled output.

Here's a script to get display modes:
https://gist.github.com/joevt/0c75b42171b3fb1a5248b4e2bee8e4d0
This is a faster script:
https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8
This is a command to get display modes and other display related info but its formatting for Apple Silicon information is not as good as its formatting for Intel Mac information:
https://github.com/joevt/AllRez/tree/main/AllRez

BetterDisplay has a command line interface. It's newer and better than the above. There's a command to list display modes. I would like to see what that looks like for both of your displays.
https://github.com/waydabber/betterdisplaycli
https://github.com/waydabber/BetterDisplay/wiki/Integration-features,-CLI
https://github.com/waydabber/BetterDisplay/issues/2646#issuecomment-1946631590
 
I'm guessing those two gists are for Intel-based Macs... they don't output anything on AppleSilicon. BetterDisplay doesn't show anything about tiling or DSC status.


So when you run the LG through the OWC hub it gains six new modes, loses its two highest-resolution modes, and the "Native" resolution is detected as "3840x2160 60Hz 10bpc" instead of "2560x1440 HiDPI 60Hz 10bpc".

This is with the very original LG 5K monitor. I was eligible for the trade-in for WiFi interference, but I never bothered because the monitor works well and didn't want to risk getting one with dead pixels.

When run through the OWC hub the LG loses:
  • 4096x2304 60Hz 10bpc
  • 5120x2880 60Hz 10bpc
The new modes it gains are:
  • 480x300 HiDPI 60Hz 10bpc Unsafe
  • 512x384 HiDPI 60Hz 10bpc Unsafe
  • 960x540 60Hz 10bpc
  • 960x600 60Hz 10bpc
  • 1024x576 60Hz 10bpc
  • 1024x768 60Hz 10bpc
So I'm guessing it's working by having MacOS scale the 5K screen image down to 3840x2160 and then the monitor upscales that back to 5K... which actually looks really really good. I'm not going to run it that way, but it is surprising that it works well and just out of the box.
 
Last edited:
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I'm guessing those two gists are for Intel-based Macs... they don't output anything on AppleSilicon.
The gists were made for Apple Silicon Macs. Maybe they need to be updated for M4.

4096x2304 60Hz 10bpc
I'm not sure why it would loose this mode but I don't think this mode is important to you anyway.

So I'm guessing it's working by having MacOS scale the 5K screen image down to 3840x2160 and then the monitor upscales that back to 5K... which actually looks really really good. I'm not going to run it that way, but it is surprising that it works well and just out of the box.
When Apple makes a Mac that can have 3 DisplayPort connections per Thunderbolt 5 port like PCs can, then that Mac will be able to use the LG UltraFine 5K fully with another display from the same Thunderbolt 5 hub or dock.
 
I got a Trebleet TB5 enclosure and put a Samsung 990 Pro 2TB SSD in it.

Somewhat interesting(although not surprising) results when hooking up stuff and recording some rough speed readings from BlackMagic. As you would expect monitors do limit the write speed to an SSD, although not enough for most people to care. From looking at this I'm guessing there is a certain amount of bandwidth dedicated to each DisplayPort tunnel. The OWC dock as a USB-A port which likely gets some dedicated bandwidth.
  • when plugged directly into the M4Pro-Mini
    • ~6300MB/s write
    • ~5800MB/s read
  • when plugged into the OWC dock by itself
    • ~6000MB/s write
    • ~5800MB/s read
  • when plugged into the OWC dock with only Samsung 5K
    • ~6000MB/s write
    • ~5800MB/s read
  • when plugged into the OWC dock with only LG 5K
    • ~4800MB/s write
    • ~5800MB/s read
  • when plugged into the OWC dock with Samsung 5K and LG 5K (LG running at 4K resolution)
    • ~4800MB/s write
    • ~5800MB/s read
 
Last edited:
I got a Trebleet TB5 enclosure and put a Samsung 990 Pro 2TB SSD in it.

Somewhat interesting(although not surprising) results when hooking up stuff and recording some rough speed readings from BlackMagic. As you would expect monitors do limit the write speed to an SSD, although not enough for most people to care. From looking at this I'm guessing there is a certain amount of bandwidth dedicated to each DisplayPort tunnel. The OWC dock as a USB-A port which likely gets some dedicated bandwidth.
I don't think USB-A takes away bandwidth unless it's actually sending/receiving data.

  • when plugged directly into the M4Pro-Mini
    • ~6300MB/s write
    • ~5800MB/s read
  • when plugged into the OWC dock by itself
    • ~6000MB/s write
    • ~5800MB/s read
Adding docks adds latency. Interesting that the write speed drops more than the read speed. I guess it makes sense since writing is more complicated than reading.

  • when plugged into the OWC dock with only Samsung 5K
    • ~6000MB/s write
    • ~5800MB/s read
  • when plugged into the OWC dock with only LG 5K
    • ~4800MB/s write
    • ~5800MB/s read
read: 5800MB/s=47Gbps.
write: 6000MB/s=48Gbps.
write: 4800MB/s=39Gbps.
difference = 9 Gbps.

Samsung 5K uses DSC ≈12 Gbps.
LG 5K does not use DSC ≈28 Gbps.

Since read is > 40 Gbps, and write is also > 40 Gbps (with DisplayPort bandwidth added) we know Thunderbolt 5 is using symmetric 40/40 Gbps mode.

Maybe Thunderbolt 5 can handle 28-9=19 Gbps DisplayPort bandwidth before having to reduce PCIe bandwidth (at least for the Trebleet/990 combo). Maximum PCIe bandwidth is < 63 Gbps (factoring 80% PCIe efficiency makes that ≈50 Gbps).

39+28=67Gbps.
Factoring PCIe efficiency of 80%:
39/0.80+28 = 76.75 Gbps.
That's more like it - it's near the 80 Gbps max of Thunderbolt 5.

When does Thunderbolt 5 switch to asymmetric 120/40 Gbps transmit/receive mode?

  • when plugged into the OWC dock with Samsung 5K and LG 5K (LG running at 4K resolution)
    • ~4800MB/s write
    • ~5800MB/s read
Samsung 5K + LG 4K = 12 + 16 Gbps = 28 Gbps. Similar bandwidth as LG 5K by itself.
 
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When run through the OWC hub the LG loses:
  • 4096x2304 60Hz 10bpc
  • 5120x2880 60Hz 10bpc
Hi @Gabebear , can you check if this is still true if you only connect the LG 5K to the OWC hub (just 1 display instead of 2)? I only have this rather old display (from 2017) but I don't want to lose native 5K.
 
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