Macbook Pro and Mini M1 Cannot output 5k resolution via Thunderbolt 3 to 2 DisplayPort Adapter

[miaotata]

I have a Dell UP2715k which requires 2 displayport 1.2 cables. On my old mac I use a monoprice thunderbolt 3 to 2 displayport adapter and can get 5k resolution. On m1 chip macs it doesn't work. It shows a weird resolution (848*480) in system info and the monitor doesn't show anything at all.

1 usb-c to displayport can get the monitor to 4k max, but it does not support high dpi. Adding another usb-c to displayport doesn't do anything (On the old mac it will switch Dell to 5k@60hz)

I read the discussions on the limitation on the new m1 macs so just an FYI.

 

[Gnattu]

M1 has only one "dp port" in concept shared by two USB-C ports, if one of the USB-C claims dp, the other can no longer claim that.

 

[miaotata]

The weird thing is that even using one of the displayports still only output 848*480.

 

[joevt]

I have a Dell UP2715K which requires 2 displayport 1.2 cables. On my old mac I use a monoprice thunderbolt 3 to 2 displayport adapter and can get 5k resolution. On m1 chip macs it doesn't work. It shows a weird resolution (848*480) in system info and the monitor doesn't show anything at all.

Strange. It works for LG UltraFine 5K and HP Z27q.
Does the Monoprice Thunderbolt 3 to Dual DisplayPort Adapter appear in the list of Thunderbolt devices?
Is the adapter connected at 40 Gbps?
Is the Dell input source set to dual DisplayPort?
Did you try both Thunderbolt ports?
Did you try swapping the two DisplayPort cables at the adapter?

M1 has only one "dp port" in concept shared by two USB-C ports, if one of the USB-C claims dp, the other can no longer claim that.

Except that people with the LG UltraFine 5K and HP Z27q have gotten 5K so it means there must be two DisplayPort connections which can be used for a single tiled display (but won't work for two separate displays).

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The weird thing is that even using one of the displayports still only output 848*480.

There's some weird things in the EDIDs of the Dell UP2715K.
Both connections have the same product ID: 40b6, I guess that's normal.
In the second EDID, all the timings non-tiled timings are removed except for a 848x380 timing that only exists in the second EDID.
The second EDID actually has the left tile, usually it has the right tile.
Both EDIDs have the timing for the tiles: 2560x2880 so it should work.

Does holding the option key and selecting "Scaled" in the Displays preferences panel show any other resolutions?

Maybe you need an EDID override. You can try using the EDID which is in the overlay property of the mtdd.
The mtdd is at /System/Library/Displays/Contents/Resources/Overrides/DisplayVendorID-10ac/DisplayProductID-40b6.mtdd
The EDID override should go in /Library/Displays/Contents/Resources/Overrides/DisplayVendorID-10ac/DisplayProductID-40b6

This is probably a bug that should be reported to Apple. Maybe they'll fix it. Or maybe they'll make it so we can't connect non-Thunderbolt tiled displays.

 

[Gnattu]

Except that people with the LG UltraFine 5K and HP Z27q have gotten 5K so it means there must be two DisplayPort connections

It is not the same thing.

One USB-C port can have multiple DP 1.2 links on it, because thunderbolt supports that mode, so you can get 2xdp1.2 from one USB-C port, but you cannot get it from BOTH. What OP was doing was that he tried using two 2 usb-c to do on two USB-C ports.

 

[joevt]

It is not the same thing.

It is the same thing. The LG UltraFine 5K takes two DisplayPorts from Thunderbolt to make 5K (two tiles of 2560x2880).
The HP Z27q takes two DisplayPort from Thunderbolt (using a Thunderbolt to Dual DisplayPort adapter) to make 5K (two tiles of 2560x2880).

One USB-C port can have multiple DP 1.2 links on it, because thunderbolt supports that mode, so you can get 2xdp1.2 from one USB-C port, but you cannot get it from BOTH. What OP was doing was that he tried using two 2 usb-c to do on two USB-C ports.

But the OP was using a single Thunderbolt to Dual DisplayPort adapter so both DisplayPort connections are to the same Thunderbolt controller.

There is a crossbar mux in the M1 Macs that connects the two DP signals to either Thunderbolt controller depending on what Thunderbolt port you connect the LG UltraFine 5K to. We are still trying to determine if the mux is able to put one DP connection to each Thunderbolt controller/port for a tiled display. I think the OP said he tried that but nothing happened so it may be that the mux cannot put one DisplayPort per controller/port - but we can't trust that until he gets two DisplayPorts on one controller/port to work, like itslice did with his HPZ27q.

 

[miaotata]

Copying from the other thread:

Finally figured out how to make it work. When first connected thunderbolt 3 to dual displayport adapter directly from new mac to my Dell UP2715k, it only outputs 848*480 for some reason. I can use apps like EasyRes to manually set my Dell to 5120*2880, but no High DPI option available.




However if i put the laptop on sleep and wake it up, it will correctly recognize my dell and shows the 5120*2880 at 2x Retina scale correctly.

It's the weirdest thing ever and I have to do it again every time I turn on my laptop but at least there is a way to make it work now.

 

[Paul F]

Hi Guys, How useable UP2715k is for M1 mini? I'm thinking of buying one. Will I constantly need to reset the screen or it is relatively stable?

 

[Fair Witness]

I have the same issue with my Dell UP2715K and my M1 Air using a CalDigit mini Dock Dual DisplayPort. The display is recognized as having a resolution of 848x480. However, if I just go to display preferences and do something like set it to rotate 90 degrees then the actual resolution is found, just need to rotate it back to 0 degrees and I'm good to go.

This continues to work in clamshell mode and everything is wonderful, however if I let the laptop go to sleep in clamshell mode, when I go to wake it up it won't recognize the Dell 5K's proper resolution anymore (and therefore I can't see anything on the Dell monitor), and I have to open the lid on the laptop and do the rotation trick again.

I have an OWC branded TB3 to dual display port adapter I'm going to try on Friday, not sure if it will make a difference or not. It definitely feels like this is something Apple could fix, as clearly the monitor does work.. once you jump thru a few hoops.

 

[miaotata]

Hi Guys, How useable UP2715k is for M1 mini? I'm thinking of buying one. Will I constantly need to reset the screen or it is relatively stable?

Unfortunately Mac mini won’t work because under the default resolution 848*480 the monitor won’t display anything so you cannot make any further changes....

 

[joevt]

Unfortunately Mac mini won’t work because under the default resolution 848*480 the monitor won’t display anything so you cannot make any further changes....

But you said the display works after putting the computer to sleep and waking it. If the computer accepts keyboard commands, then Control-Eject and press S can put the computer to sleep?

 

[miaotata]

But you said the display works after putting the computer to sleep and waking it. If the computer accepts keyboard commands, then Control-Eject and press S can put the computer to sleep?

Doesn't work on Mini unfortunately. Can't really tell what's going on since I cannot see any output. Maybe attaching a 2nd HDMI monitor might help. Can't test it now since I don't have a 2nd monitor...

 

[Paul F]

Hmm, that's weird... I guess the only way is to try it out really. Dell has multiple revisions of this display. I don't understand why it doesn't work on Mini if it works on Air...

 

[miaotata]

Hmm, that's weird... I guess the only way is to try it out really. Dell has multiple revisions of this display. I don't understand why it doesn't work on Mini if it works on Air...

I think it only works if I put it to sleep using battery only on Macbook. Can't really do that on Mini. I don't know why.

There is one other way to make it work: Rotate the display under Settings. Not sure how I can do that on Mini without seeing the screen. Is there a command line or shortcut to do that?

 

[KPOM]

Hi Guys, How useable UP2715k is for M1 mini? I'm thinking of buying one. Will I constantly need to reset the screen or it is relatively stable?

If you need a 5K display, your best bet is the LG UltraFine 5K. I have that monitor (the 2019 version) and it works just fine with my M1 MacBook Air using a Thunderbolt cable.

 

[joevt]

There is one other way to make it work: Rotate the display under Settings. Not sure how I can do that on Mini without seeing the screen. Is there a command line or shortcut to do that?

Not sure about a command.
What about screen sharing to see what's happening? Does that work on M1 Macs to share with an Intel Mac?

 

[miaotata]

Just tried. Remote connection does get Dell UP2715K to 5k resolution on Mac Mini (change rotation to 90 and back) but it is a pain in the ass to use another mac to connect to it first and then switch back and forth every time it wakes up.

 

[joevt]

Just tried. Remote connection does get Dell UP2715K to 5k resolution on Mac Mini (change rotation to 90 and back) but it is a pain in the ass to use another mac to connect to it first and then switch back and forth every time it wakes up.

Maybe with SwitchResX, you can make an AppleScript? I tried pressing Record in Script Editor.app, then rotated the screen back and forth. The following appeared:

tell application "SwitchResX Daemon"
	activate
	set orientation of display 1 to 90
	set orientation of display 1 to 0
end tell

Well, maybe it won't work in the current version of SwitchResX on an M1 Mac (because I think I read somewhere that it doesn't support rotation yet?).

 

[miaotata]

I don't see the rotation function in the latest beta of SwitchResX. Maybe the next version? BTW even if this works I still need to find another Mac to connect to the Mini first. I will open a case with Apple as I think this might be a bug.

 

[Paul F]

I don't see the rotation function in the latest beta of SwitchResX. Maybe the next version? BTW even if this works I still need to find another Mac to connect to the Mini first. I will open a case with Apple as I think this might be a bug.

What's the revision of your DELL display? It should be written on a back where all ports are.

 

[petterihiisila]

If you need a 5K display, your best bet is the LG UltraFine 5K. I have that monitor (the 2019 version) and it works just fine with my M1 MacBook Air using a Thunderbolt cable.

I've got the the same setup, works fine as 5k in clamshell. For the two other displays I'm planning to test a DisplayLink dock next week.

System Information > Graphics/Displays:

Chipset Model: Apple M1 (8 core GPU)
Type: GPU
Bus: Built-In
Total Number of Cores: 8
Vendor: Apple (0x106b)
Metal Family: Supported, Metal GPUFamily Apple 7
Displays:

LG UltraFine:
Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
UI Looks like: 2560 x 1440 @ 60Hz
Main Display: Yes
Mirror: Off
Online: Yes
Rotation: Supported
Automatically Adjust Brightness: Yes

 

[joevt]

What's the revision of your DELL display? It should be written on a back where all ports are.

My Dell UP2715K is REV A01 from Apr 2015 but I don't have an M1 Mac to test. Are there multiple revisions? They didn't make the display for very long.

 

[miaotata]

Mine is Rev A01 from July 2015

 

[raknor]

It is the same thing. The LG UltraFine 5K takes two DisplayPorts from Thunderbolt to make 5K (two tiles of 2560x2880).
The HP Z27q takes two DisplayPort from Thunderbolt (using a Thunderbolt to Dual DisplayPort adapter) to make 5K (two tiles of 2560x2880).

Fundamentally the same but not quite. The LG UltraFine tunnels 8 DP 1.2 lanes in one thunderbolt cable. So how the Primary (EDID with all the tiled timings) and secondary tiles (with the 848x480 timing) hot plugs show up is different than the Dell UP2715K which uses two display port cables.

But the OP was using a single Thunderbolt to Dual DisplayPort adapter so both DisplayPort connections are to the same Thunderbolt controller.

There is a crossbar mux in the M1 Macs that connects the two DP signals to either Thunderbolt controller depending on what Thunderbolt port you connect the LG UltraFine 5K to. We are still trying to determine if the mux is able to put one DP connection to each Thunderbolt controller/port for a tiled display. I think the OP said he tried that but nothing happened so it may be that the mux cannot put one DisplayPort per controller/port - but we can't trust that until he gets two DisplayPorts on one controller/port to work, like itslice did with his HPZ27q.

In the two cable case there are two separate DP tunnels over thunderbolt get created with 4 lanes each. So the timing at which the tiles come up are not the same and if the secondary tile shows up first the system will think one 848x480 display came up and ignore the second one.

If the primary tile shows up it probably figures out the second hot plug is for the secondary tile and stitches the display to 5K like the thunderbolt versions. There is some magic the M1 is doing that allows one display it supports to work with multi tiled displays.

That's why the sleep wake and rotation tricks work they tear down the DP links on thunderbolt and reconnect this results in the primary tile coming online first sometimes and not the other times.

 

[joevt]

I've got the the same setup, works fine as 5k in clamshell. For the two other displays I'm planning to test a DisplayLink dock next week.

System Information > Graphics/Displays:

Chipset Model: Apple M1 (8 core GPU)
Type: GPU
Bus: Built-In
Total Number of Cores: 8
Vendor: Apple (0x106b)
Metal Family: Supported, Metal GPUFamily Apple 7
Displays:

LG UltraFine:
Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
UI Looks like: 2560 x 1440 @ 60Hz
Main Display: Yes
Mirror: Off
Online: Yes
Rotation: Supported
Automatically Adjust Brightness: Yes

Only the frame buffer size is shown in System Information > Graphics/Displays. It says 5120 x 2880 but it could be outputting something else, like 4K.
The ioreg will show the current output resolution.

Fundamentally the same but not quite. The LG UltraFine tunnels 8 DP 1.2 lanes in one thunderbolt cable. So how the Primary (EDID with all the tiled timings) and secondary tiles (with the 848x480 timing) hot plugs show up is different than the Dell UP2715K which uses two display port cables.

In the two cable case there are two separate DP tunnels over thunderbolt get created with 4 lanes each. So the timing at which the tiles come up are not the same and if the secondary tile shows up first the system will think one 848x480 display came up and ignore the second one.

If the primary tile shows up it probably figures out the second hot plug is for the secondary tile and stitches the display to 5K like the thunderbolt versions. There is some magic the M1 is doing that allows one display it supports to work with multi tiled displays.

That's why the sleep wake and rotation tricks work they tear down the DP links on thunderbolt and reconnect this results in the primary tile coming online first sometimes and not the other times.

There is no such thing as 8 lanes of DisplayPort. Max lanes is 4, even when using Thunderbolt.

Look at the iMac 5K display or LG 5K display with the AGDCDiagnose command on an intel Mac. It shows two 4 lane connections of HBR2 (DisplayPort 1.2) just like it does for a Dell UP2715K or a HP Z27q. Doesn't matter if they go through Thunderbolt or not. The DisplayPort connections are separate.

I agree that the DisplayPort connections may occur at different times or appear in a different order or have tile info specified in the EDID in a different way, but Apple has handled these issues ever since they added support for multi tiled-displays a long time ago. They mention these same displays in their support documents (have to find them on the wayback machine now). For example, with the Dell or HP display, I can connect either cable, then connect the other cable any time later to get 5K. The order and timing do not matter. The system gets the EDID for one connection, then when it gets the EDID of the other connection, it can see that all tiles are connected, then create the single spanning frame buffer.

This flaky behaviour we're seeing on M1 Macs is a regression in functionality caused by a change of the graphics system (it's using iPhone graphics instead of Mac graphics) and Apple's inadequate testing.