Daisy chaining LG UltraFine 5K through Apple Studio Display XDR with MacBook Pro (M5 Pro)

[jim468]

Hello, I recently purchased an Apple Studio Display XDR and I’m using it with a MacBook Pro (M5 Pro). I also have an LG UltraFine 5K display.

I’m trying to daisy chain the LG UltraFine 5K through the Studio Display XDR (i.e. put LG at the end of a daisy chain), but it does not work. The LG display functions correctly when connected directly to a port on the MacBook Pro, but it is not recognized when connected through the Studio Display XDR.

At the Apple Store, I observed that a MacBook Pro (M5 Pro) could drive the Studio Display XDR and daisy chain to another standard Apple Studio Display, but this setup does not seem to work with the LG UltraFine 5K.

Has anyone else attempted a similar configuration or encountered this issue? Any insights or suggestions would be appreciated. Thanks

 

[PaulD-UK]

@jim468 "I’m trying to daisy chain the LG UltraFine 5K through the Studio Display XDR (i.e. put LG at the end of a daisy chain), but it does not work."

The LG 5K Ultrafine monitor originated when Apple introduced Thunderbolt 3 to the Mac range - specifically to get a single cable capable of driving a 5K/60 monitor.

Before that, to work at 5K with the Mac Pro 6.1 trash can, Apple had collaborated with LG for Dell to come up with the UP2715K 5K/60 monitor. But to work with the DP 1.2's 4K/30 standard that Mac GPUs of that era used, the only way to get 5K/60 was to use two separate DP 1.2 cables connecting the Mac Pro to the UP2715K.

When Apple introduced TB 3, they devised their own software mode, where a single TB 3 cable could carry two simultaneous DP 1.2 video streams - one each for left and right halves of the full 5K/60 video stream.

And throughout it's production run LG manufactured the 5K Ultrafine to work in this TB 3 dual-stream mode.
The later models could also work with a single video stream in USB-C Alt-mode, but that could only manage 4K/60.

From about 2020, and with all Apple Silicon Macs, Macs now run on the DP 1.4 or DP 2.1 standard, which can support up to 8K video, and all modern high res monitors work fine with a single cable.

But that leaves your LG 5K Ultrafine as a relic of the past.
It 'should' work fine when connected to a Mac by TB 3 or higher.
It might even work as you are trying to achieve - in a daisy-chain connected to a Studio XDR monitor - IF there was an M5 Mac Studio (with full bandwidth TB 5 ports) to try connecting it to? Maybe, maybe not...

But the TB 4 ports of your M5 MBP can only just manage the bandwidth requirements of your Studio XDR - and that is using DSC compression.

There is no possible way to daisy-chain the LG 5K Ultrafine, because even on its own, that monitor requires two streams of uncompressed TB 3 video data to produce a 5K picture.

Your LG monitor has had a good run, but with current gear, its time has run out... 😉

 

[jim468]

Thank you @PaulD-UK , appreciate the insight!

It seems like the time for LG has indeed run out. I do see random crashes when my MacBook wakes up from sleep. Upon looking at the logs, seems like the display driver crashes while waiting to do a handshake with the LG display as it takes longer than expected.

ChatGPT recommends to set 'wake for network access' to 'Never' under Settings on Mac to prevent this handshake and subsequent crash during the low-power state. So I am trying that out now.

 

[thenewepic]

But the TB 4 ports of your M5 MBP can only just manage the bandwidth requirements of your Studio XDR - and that is using DSC compression

What do you mean? The OP has M5 Pro MacBook Pro which is equipped with TB5 ports.

I’m trying to daisy chain the LG UltraFine 5K through the Studio Display XDR (i.e. put LG at the end of a daisy chain), but it does not work

It’s very interesting because M5 Pro should in theory support such a setup. At least I thought so.
Do USB-C ports on the LG work while being connected? Or nothing works at all?

 

[jim468]

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[jim468]

It’s very interesting because M5 Pro should in theory support such a setup. At least I thought so.

M5 Pro does support it - assuming the monitor is connected directly to the computer.

LG Ultrafine 5K requires two simultaneous DP 1.2 video streams to render content on the screen. The Studio Display/XDR does not provide two simultaneous video streams downstream via Daisy Chain.

Do USB-C ports on the LG work while being connected? Or nothing works at all?

I do not recall checking this, however power was being supplied to connected peripherals.

 

[jim468]

ChatGPT recommends to set 'wake for network access' to 'Never' under Settings on Mac to prevent this handshake and subsequent crash during the low-power state. So I am trying that out now.

This worked. Now the system does not crash when I wake it up from sleep in the morning.

 

[thenewepic]

The Studio Display/XDR does not provide two simultaneous video streams downstream via Daisy Chain

didn't know this.

 

[joevt]

M5 Pro does support it - assuming the monitor is connected directly to the computer.

LG Ultrafine 5K requires two simultaneous DP 1.2 video streams to render content on the screen. The Studio Display/XDR does not provide two simultaneous video streams downstream via Daisy Chain.

The DP 1.2 streams come from the host Mac, not the Studio Display XDR.
The Studio Display takes one DisplayPort connection.
The LG takes two DisplayPort connections.

A DisplayPort connection (or tunnel) is created between a DisplayPort In Adapter of the host Thunderbolt controller and a DisplayPort Out Adapter of the Thunderbolt controller in the display.

Use this command to check how many DisplayPort In Adapters your Mac's Thunderbolt controllers have, vs the DisplayPort Out Adapters of the displays:

ioreg -fiw0 > ioregM5Pro.txt

The Apple Studio Display XDR supports a dual tile mode like the LG UltraFine 5K display but the Apple Studio Display XDR usually works with a single tile when connected to a Mac that supports DSC (and the dual tile mode only support 60 Hz like on the LG UltraFine 5K).

Hopefully, the host Mac's Thunderbolt 5 controller supports 3 DisplayPort tunnels and is smart enough not to creating two DisplayPort tunnels to the Apple Studio Display XDR.

 

[joevt]

If the XDR is using two DisplayPort tunnels, then you can maybe force it to use a single DisplayPort tunnel by connecting it as USB-C only (with a 10 Gbps cable), but then you can't use the Thunderbolt features of the display.

If it tries to connect as Thunderbolt 20 Gbps with the USB-C cable, then it might still get two DisplayPort tunnels. In that case, you would need to use a DisplayPort to USB-C cable to completely eliminate the possibility of a Thunderbolt connection or connect to a hub that provides a USB-C with DisplayPort Alt Mode connection without Thunderbolt, such as the HP Thunderbolt Dock G2.