Boot Camp Second Thunderbolt Monitor in daisy chain Not Working

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Level 1

8 points

Boot Camp Second Thunderbolt Monitor in daisy chain Not Working

So I have an odd problem and cannot seem to find anyone else that has the same issue. My old setup was a 2015 MacBook Pro 15" with two Apple Thunderbolt Displays daisy chained together. My Boot Camp install runs just fine with both displays detected and working within Windows.

I recently upgraded to a 2018 MacBook Pro 15" with Touch Bar and purchased the Apple Thunderbolt 3 to Thunderbolt 2 adapter to be able to connect the monitors. Under macOS, both Thunderbolt displays and the internal laptop display are detected and show up normal. However, if I reboot into Windows 10 then my second Thunderbolt display does not show up and Windows cannot see it.

Troubleshooting steps I've tried.

-Reinstalling Boot Camp drivers.

-Updated AMD graphics driver.

-Tried different MacBook ports.

-Plugged each monitor in individually (each one works fine).

-Switching which monitor plugs into the laptop vs the other monitor (see below).

My current setup is Monitor 1 connects to the MacBook and Monitor 2 connects to Monitor 1. Monitor 1 also has Ethernet and USB peripherals connected.

If I connect Monitor 2 to the MacBook and Monitor 1 to Monitor 2, I will get a display on Monitor 2 but not Monitor 1. However, Monitor 1 is being detected because my Ethernet will USB peripherals show up and work.

I am not sure if this is a driver issue, using the T3 to T2 adapter, or something else. Any information and suggestions would be greatly appreciated!

MacBook Pro with Touch Bar

Posted on Sep 10, 2019 1:15 PM

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Answer 1

Loner T

Level 9

59,536 points

Sep 12, 2019 9:14 AM in response to m_stew

Both displays are connected to the same TB bus(TB1). If you move the cable on the Mac end to a different USBc port, does the TB bus change to TB0?

We should also check how the TB displays show up in Windows, similar to the macOS. In Windows, you seem to be running SST, while macOS is a MST chain. This would also explain that the DP packets only show up on the last display in the chain, while non-DP packets are on both displays, allowing the first TB display to still perform hub functions.

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Answer 2

Loner T

Level 9

59,536 points

Sep 11, 2019 4:43 AM in response to m_stew

The T2-3-to-T2 adapter does not support daisy-chaining. You may want to connect each monitor directly to the 2018 Mac.

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Answer 3

Loner T

Level 9

59,536 points

Sep 12, 2019 1:28 PM in response to m_stew

Do you have two USBC(TB3)-to-TB2 adapters, or can you borrow one temporarily?

Also, see "Duplicate these displays" not supported in Boot Camp running Windows 8.1 or Windows 10 - Apple Support which only references 4K, but you do not have a 4K display.

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Answer 4

Loner T

Level 9

59,536 points

Sep 14, 2019 6:20 AM in response to stewblack23

stewblack23 wrote:

I'm having this exact same issue with my late 2012 Mac Mini in bootcamp 6 running Windows 10.

The GPUs are different. If the corresponding Windows driver cannot detect and handle MST, you will not be able to use daisy chaining in Windows.

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Answer 5

Loner T

Level 9

59,536 points

Sep 12, 2019 7:35 AM in response to m_stew

Can you post the same screen for Thunderbolt? The connection is a DP connection, so Windows driver needs to support DP 1.2 and MST.

Also, see Use 4K displays, 5K displays, and Ultra HD TVs with your Mac - Apple Support, even though the Apple TB is not 4K/5K.

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Answer 6

Loner T

Level 9

59,536 points

Sep 11, 2019 2:59 PM in response to m_stew

In macOS, when both displays are active, can you post a screen shot of the About This Mac -> System Report -> Graphics/Displays? We should check what are the protocols used for the displays.

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Answer 7

m_stew Author

Level 1

8 points

Sep 12, 2019 1:35 PM in response to Loner T

I did borrow an adapter and when I plug both monitors in individually then all the displays work.

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Answer 8

m_stew Author

Level 1

8 points

Sep 12, 2019 1:14 PM in response to Loner T

EDIT: I guess I added too many photos. You can still see them if you right click and open in a new tab.

Yes, it seems that both TB ports on the left side are tied to TB0 and both ports on the right are with TB1.

Regarding what Windows sees, it is still just the internal display and whichever TB display is connected first.

The AMD control panel also shows the same information as Windows Settings.

I then checked Speccy to see if it saw anything else with the monitors but it doesn't seem so.

An interesting bit of information I found out is that the speakers of both monitors are detected.

Information from GPU-Z. I don't know if this will help but I will provide it anyway.

More Speccy. It appears that everything from both monitors is detected except the second display will not appear.

Thunderbolt driver version if it helps.

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Answer 9

Loner T

Level 9

59,536 points

Sep 16, 2019 8:08 AM in response to m_stew

m_stew wrote:

I was afraid of that. Would that be a problem for AMD to resolve?

Yes.

I suppose I can use two T3 to T2 adapters for now to retain functionality.

Yes, it is a simpler solution. It also allows one monitor to be disconnected, without impacting the other.

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Answer 10

Loner T

Level 9

59,536 points

Sep 12, 2019 1:36 PM in response to m_stew

The Bootcamp driver does not seem to support MST, but I have no way to verify it.

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Answer 11

m_stew Author

Level 1

8 points

Sep 11, 2019 8:33 AM in response to Loner T

I don't mean to sound dense, but if daisy chaining is not supported on the adapter then why does it work if I boot the 2018 MBP into macOS? Also, why is it that when I plug the monitor with Ethernet and peripherals into the other monitor I can get an Ethernet connection and use the mouse and keyboard? It seems to me like it is more of a software issue rather than hardware.

If the adapter truly is not supported for daisy chaining and macOS working is a fluke, are there any other adapters that provide daisy chaining support? I also bought a StarTech dock for the new MBP so that I could have a one wire docking solution. I would like to try and avoid having to plug in two cables to make the setup work if possible.

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Answer 12

Sep 13, 2019 10:11 PM in response to Loner T

I'm having this exact same issue with my late 2012 Mac Mini in bootcamp 6 running Windows 10. I have two Apple 27 inch Thunderbolt displays daisy chained together. Works great on macOS but on bootcamp 6 running Windows 10 Pro 1903 only the display plugged directly into the thunderbolt ports works. And since I only have one Thunderbolt port cant plug both in the Mac Mini at the same time.

And ideas would be greatly appreciated!

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Answer 13

m_stew Author

Level 1

8 points

Sep 16, 2019 8:11 AM in response to Loner T

Loner T wrote:

Yes, it is a simpler solution. It also allows one monitor to be disconnected, without impacting the other.

Yeah, but the main point was for a single T3 wire that connected the MBP to the dock and subsequently both monitors without having to connect/disconnect multiple cables when taking the laptop.

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