How many monitors do M1 Pro/Max support without HDMI?

[Fomalhaut]

the HDMI port on the current MacBook Pros is only HDMI2 (because Apple ran out of bandwidth on the SOC and HDMI is less important) and not HDMI 2.1, which is lower bandwidth than the Thunderbolt 4 ports can handle - which means lower refresh rate than you can get out of a Thunderbolt 4 port at very high resolutions (above 4k).

I think it tops out at 4k/60 (or something like that) and the TB4 can go higher (e.g., 4k/120, 8k/60 or 8k/120 not sure).

If you've got a normal person monitor then sure, the HDMI 2.0 port is fine. And yeah, use it (I'm using mine right now) - HDMI cables/ports on monitors are far more common than type C USB, and it's one less dongle if your. monitor doesn't have USB-C directly.

Thanks. I’m very much in the category of having “normal person monitors”, hence my curiosity at @Pro Apple Silicon ’s comment that HDMI is for “emergencies only”. It look fine for me for the next 10 years

 

[throAU]

Yeah, "emergencies only" is very much a stretch.

Its for *convenience*.

TVs, Projectors, other random displays you may need to plug into to show a client something will almost always (in 2021) have a HDMI port if nothing else.

 

[x3n0n1c]

You guys also have to keep in mind that Apple designs in chips years in advance, and the HDMI 2.1 spec is very new and is still in flux. If it wasn't ready for the time they locked in the silicon design then it wouldn't make it into the chip.

This is one of the downsides of everything being integrated into the SoC and not done by discrete components as they can be updated much further into the process.

 

[joevt]

the HDMI port on the current MacBook Pros is only HDMI2 (because Apple ran out of bandwidth on the SOC and HDMI is less important)

"Run out of bandwidth on the SOC" makes no sense. There is no bandwidth problem if no other displays are connected.

and not HDMI 2.1, which is lower bandwidth than the Thunderbolt 4 ports can handle - which means lower refresh rate than you can get out of a Thunderbolt 4 port at very high resolutions (above 4k).

I think it tops out at 4k/60 (or something like that) and the TB4 can go higher (e.g., 4k/120, 8k/60 or 8k/120 not sure).

"HDMI 2.1, which is lower bandwidth than the Thunderbolt 4 ports can handle" did you mean HDMI 2.0 (which is 14.4 Gbps)?
Or did you mean "HDMI 2.1 is higher bandwidth than the thunderbolt 4 ports can handle" (since HDMI 2.1 can go up to 42.67 Gbps).

If you've got a normal person monitor then sure, the HDMI 2.0 port is fine. And yeah, use it (I'm using mine right now) - HDMI cables/ports on monitors are far more common than type C USB, and it's one less dongle if your. monitor doesn't have USB-C directly.

Normal person monitor means something less than 4K60 HDR since HDMI 2.0 can't do 4K60 10bpc without resorting to 4:2:0.

You guys also have to keep in mind that Apple designs in chips years in advance, and the HDMI 2.1 spec is very new and is still in flux. If it wasn't ready for the time they locked in the silicon design then it wouldn't make it into the chip.

This is one of the downsides of everything being integrated into the SoC and not done by discrete components as they can be updated much further into the process.

But it's not the SoC that generates the HDMI signal.
There's a MegaChips (or Kinetic Technologies now) MCDP2920 DisplayPort-to-HDMI Converter.
https://www.ifixit.com/Guide/MacBook+Pro+14-Inch+2021+Chip+ID/145718

I thought they could have used the same HDMI 2.1 chip that the Apple TV uses, but apparently the Apple TV uses the same HDMI 2.0 chip and the only HDMI 2.1 feature that the Apple TV supports is eARC
https://www.ifixit.com/Teardown/Apple+TV+4K+2021+Teardown/142845?permalink=1#comment-743358

Maybe the existing DisplayPort 1.4 to HDMI 2.1 chips (Synaptics VMM6100 and Realtek RTD2173) are not sufficient for Apple's needs
https://forums.macrumors.com/thread...ransfers-recommendation.2278473/post-29466205

 

[Pro Apple Silicon]

Thanks. I’m very much in the category of having “normal person monitors”, hence my curiosity at @Pro Apple Silicon ’s comment that HDMI is for “emergencies only”. It look fine for me for the next 10 years

I said convenience. Not "emergencies". This is your made-up contribution. And no one really cares if you choose to use the HDMI port as primary output. Just don't expect it to be as capable as the 3 ports that are there for that reason: to be capable.

Yeah, "emergencies only" is very much a stretch.

Its for *convenience*.

TVs, Projectors, other random displays you may need to plug into to show a client something will almost always (in 2021) have a HDMI port if nothing else.

 

[Fomalhaut]

I said convenience. Not "emergencies". This is your made-up contribution. And no one really cares if you choose to use the HDMI port as primary output. Just don't expect it to be as capable as the 3 ports that are there for that reason: to be capable.

Fair enough, but I still haven’t had a complete answer to my question of whether there are any real advantages to using the TB4 ports for people without high end monitors. If I have a monitor with 4K/60Hz or less, without USB-C connectors, power delivery or a USB hub, what are the advantages of connecting via TB4?

A Ferrari is more capable than a Camry but they both go the same speed in a 50km/h surburban street…

 

[bill-p]

If I have a monitor with 4K/60Hz or less, without USB-C connectors, power delivery or a USB hub, what are the advantages of connecting via TB4?

Because you're more likely to run into this issue with HDMI, I think:

Anyone have a monitor that can run in RGB color mode with Mac Mini M1?

If so, pls list brand, model and connection type. I can’t get my Dell U2720Q to run in RGB color mode (YPbPr only) and would like to know which monitors can actually run RGB color mode with Mac Mini M1. Thx

forums.macrumors.com

For some weird reason, MacOS seems to prefer to treat anything connected to HDMI as a TV, and then tries to do YUV over RGB. I certainly have seen this myself when trying to connect to my LG CX. It took a Thunderbolt -> DisplayPort 1.4 -> HDMI 2.1 adapter to fix.

What it'll look like is slight... banding in highlights and darker scenes. As if the bit depth of the display took a nose dive. But in reality, RGB values just aren't being mapped to YUV properly. There are software fixes proposed in the thread I linked above, but I'd prefer a hardware adapter anyway.

 

[throAU]

Fair enough, but I still haven’t had a complete answer to my question of whether there are any real advantages to using the TB4 ports for people without high end monitors. If I have a monitor with 4K/60Hz or less, without USB-C connectors, power delivery or a USB hub, what are the advantages of connecting via TB4?

A Ferrari is more capable than a Camry but they both go the same speed in a 50km/h surburban street…

There aren’t any. More to the point…

The hdmi port only does video, the other ports can be used for other stuff. If your monitor is hdmi and isn’t hamstrung by the hdmi2.0 spec, definitely use it and keep the type c ports free for other stuff that isn’t video!

 

[Fomalhaut]

There aren’t any. More to the point…

The hdmi port only does video, the other ports can be used for other stuff. If your monitor is hdmi and isn’t hamstrung by the hdmi2.0 spec, definitely use it and keep the type c ports free for other stuff that isn’t video!

To answer my own question, I found this:

DisplayPort over USB-C - DisplayPort

www.displayport.org

Why More and More Video Monitors Are Relying on USB-C

Just when it seemed that we’d all settled on one industry standard video input/output to make use of, along comes another one to complicate matters—you’ll

gizmodo.com

Pretty much what I thought. If you have a monitor that can take advantage of the improved standard, then connecting to it via USB-C/TB4 will give you more features.

I don't have such monitors yet, so for me, simply using the HDMI 2.0 port will not disadvantage me.

 

[marstan]

There is another limitation of HDMI 2.0: It can't output 10-bit color at 4k60; only 8 bit at that resolution. Not a issue for most people but a limitation for those that work at very high levels of image quality. And 10-bit color can only be achieved if the entire hardware and software chain allows it: 10-bit display, interface (TB/displayport), GPU, OS and application.

 

[joevt]

There is another limitation of HDMI 2.0: It can't output 10-bit color at 4k60; only 8 bit at that resolution. Not a issue for most people but a limitation for those that work at very high levels of image quality. And 10-bit color can only be achieved if the entire hardware and software chain allows it: 10-bit display, interface (TB/displayport), GPU, OS and application.

Right. And 10bpc is required for HDR (at least the way Apple does it?)
You can do 4K60 10bpc using 4:2:2 or 4:2:0 but that reduces the quality of the output and Apple doesn't have a method to let you choose between 8bpc and 10bpc 4:2:2.

 

[tlnargi]

There is another limitation of HDMI 2.0: It can't output 10-bit color at 4k60; only 8 bit at that resolution. Not a issue for most people but a limitation for those that work at very high levels of image quality. And 10-bit color can only be achieved if the entire hardware and software chain allows it: 10-bit display, interface (TB/displayport), GPU, OS and application.

Damn! That’s a wasted port for me and another TB down.

 

[pshufd]

With 3 x TB4 and 1 x HDMI 2.0, a maximum of two external displays on the M1 Pro seems like a surprising limitation.

Heck, my mid-2014 MBP, with 2 x TB2 and 1 x HDMI 1.4, can drive three external displays. I.e., it can drive displays from each of its video-capable ports.

Yup. I tested that myself many years ago. You can drive three external displays and also run the internal display despite Apple stating that they support two external displays.

I regret not getting the MAX as I have 3x4k but I have an M1 mini to go with the M1 PRO and the two system can drive my 3 4k monitors. The extra CPU and RAM won't hurt either.

 

[Kier-XF]

Has anyone had any luck running three monitors on an M1 Max off a dock with a single connection to the laptop

I have proved I can run three displays with three separate TB to HDMI cables, but the dock I tried so far only supported two downstream monitors, even though it had 3 downstream TB4 ports

I'm running three external 5k displays in addition to the built-in display, and each requires its own port. Attaching two or more to a Thunderbolt 4 hub will activate only one of the connected displays. Thunderbolt 4 supports two 4k displays over a hub, or theoretically you could run three lower resolution displays off the same hub, but if you're after retina resolutions you're never going to manage that with a single connection to the Mac. Unfortunately.

 

[Amethyst1]

I'm running three external 5k displays in addition to the built-in display, and each requires its own port.

What 5K displays?

 

[Kier-XF]

For the sake of interest, here is the M1 Max running internal display plus 3 5k over Thunderbolt, 4k over HDMI and a 12.9" iPad Pro with Sidecar, though I note that the 4k display is only running at 30Hz - not sure what's causing that just yet.

 

[Kier-XF]

... I think maybe the P2415Q only supports 30Hz over HDMI, rather than anything being limited at the MacBook end.

 

[Amethyst1]

For the sake of interest, here is the M1 Max running internal display plus 3 5k over Thunderbolt,

If these three are actually running at 5K (via “dual-link SST”) that implies six DisplayPort connections for them plus a seventh for HDMI.

... I think maybe the P2415Q only supports 30Hz over HDMI,

All P2415Qs manufactured in March 2016 or later can do 60 Hz via HDMI 2.0 — but that has to be enabled manually.

 

[joevt]

For the sake of interest, here is the M1 Max running internal display plus 3 5k over Thunderbolt, 4k over HDMI and a 12.9" iPad Pro with Sidecar, though I note that the 4k display is only running at 30Hz - not sure what's causing that just yet.

Please post an ioreg -fliw0 > ioreg_m1maxed.txt for this setup? zip the result in the Finder and attach. The output should be able to show if it's using 7 DisplayPort connections (2 per 5K and one for the HDMI) and what the current resolutions are. I am also curious about the PCIe setup - it has 3 Thunderbolt 4 ports now so it could have 4 or 5 PCIe domains.

 

[Kier-XF]

Unfortunately, my P2415Q is an old model and won't support 4K/60 over HDMI, and I'm afraid I can't lug this whole setup to the vicinity of a 4K TV at this moment, but here is the system report for the connected displays, along with ioreg output for @joevt to decipher.

 

[joevt]

Unfortunately, my P2415Q is an old model and won't support 4K/60 over HDMI, and I'm afraid I can't lug this whole setup to the vicinity of a 4K TV at this moment, but here is the system report for the connected displays, along with ioreg output for @joevt to decipher.

Thanks for that. There's some interesting info.

Here's the PCIe info:

 00:00.0-[02]      g4x2 > g1x1
  02:00.0          g2x1          wlan
  02:00.1          g2x1          bluetooth-pcie
 00:01.0-[01]      g4x2 > g1x1
  01:00.0          g2x1 > g1x1   pcie-sdreader

00:00.0-[01-80]    g1x16 > g1x1  pcic0 (Thunderbolt port)
 01:00.0-[02-80]   g1x4          LG UltraFine 5K Alpine Ridge
  02:01.0-[03-80]  g3x4 > g2x1
   03:00.0         g2x1          FL1100

00:00.0-[01-80]    g1x16 > g1x1  pcic1 (Thunderbolt port)
 01:00.0-[02-80]   g3x4 > g1x4   LG UltraFine 5K Titan Ridge
  02:02.0-[03-80]  g1x4
   03:00.0         g1x4          Titan Ridge USB controller

00:00.0-[01-80]    g1x16 > g1x1  pcic2 (Thunderbolt port)
 01:00.0-[02-80]   g1x4          LG UltraFine 5K Alpine Ridge
  02:01.0-[03-80]  g3x4 > g2x1
   03:00.0         g2x1          FL1100

There's one PCIe domain for the internal devices and one PCIe domain per Thunderbolt port. 4 domains total. See how there's more than one device with pcie address 00:00.0.
I wonder why they limited the number of buses per Thunderbolt domain to 128? I suppose that's at least better than what an Intel Mac can do since Intel Macs have all Thunderbolt ports and devices in the same domain.

It does appear that it's creating a second display port connection for each LG UltraFine 5K display (6 total + 1 for HDMI). All the LG UltraFine 5K displays are using a tiled mode.

Here's a list of the timing modes and current resolution for each display (using my ioreg.pl script https://gist.github.com/joevt/0c75b42171b3fb1a5248b4e2bee8e4d0 ):

Spoiler

MacBookPro18,4

disp0 = built in display
dispext0 = LG UltraFine 5K 5b11 (from 2017 week  5) 469.18MHz new model
dispext1 = LG UltraFine 5K 5b11 (from 2019 week  3) 469.18MHz new model
dispext2 = LG UltraFine 5K 5b74 (from 2019 week 10) 497.61MHz old model Why is this 497.61MHz instead of 483.37MHz? The horizontal backporch has increased from 120 to 200
dispext3 = Dell P2415Q from 2015 week 4

time perl -CSDA -Mutf8 -0777 "$scripts"/ioreg.pl < ioreg_m1max.24gpu.64gb.2tb.txt

disp0:
 -> 3024x1964@120.000Hz 259.201kHz 804.56MHz  h(8 32 40 +)  v(102 8 86 +)   (preferred)
    3024x1964@60.000Hz 259.201kHz 804.56MHz  h(8 32 40 +)  v(102 8 86 +)   (promoted)
    3024x1964@48.000Hz 259.201kHz 804.56MHz  h(8 32 40 +)  v(102 8 86 +)   (promoted)
    3024x1964@59.940Hz 258.941kHz 803.75MHz  h(8 32 40 +)  v(102 8 86 +)   (promoted)
    3024x1964@47.952Hz 258.941kHz 803.75MHz  h(8 32 40 +)  v(102 8 86 +)   (promoted)
    3024x1964@50.000Hz 259.200kHz 804.56MHz  h(8 32 40 +)  v(534 8 86 +)   (promoted)

dispext0:
    640x480@60.000Hz 0.000kHz 0.00MHz  h(16 64 80 -)  v(3 4 13 +)   (virtual)
    800x600@60.000Hz 0.000kHz 0.00MHz  h(32 80 112 -)  v(3 4 17 +)   (virtual)
    1024x768@60.000Hz 0.000kHz 0.00MHz  h(48 104 152 -)  v(3 4 23 +)   (virtual)
    1280x720@60.000Hz 0.000kHz 0.00MHz  h(64 128 192 -)  v(3 5 20 +)   (virtual)
    1280x768@60.000Hz 0.000kHz 0.00MHz  h(64 128 192 -)  v(3 7 20 +)   (virtual)
    1280x1024@60.000Hz 0.000kHz 0.00MHz  h(80 136 216 -)  v(3 7 29 +)   (virtual)
    1400x1050@60.000Hz 0.000kHz 0.00MHz  h(88 144 232 -)  v(3 4 32 +)   (virtual)
    1680x1050@60.000Hz 0.000kHz 0.00MHz  h(104 176 280 -)  v(3 6 30 +)   (virtual)
    1600x1200@60.000Hz 0.000kHz 0.00MHz  h(112 168 280 -)  v(3 4 38 +)   (virtual)
    1920x1080@60.000Hz 0.000kHz 0.00MHz  h(128 200 328 -)  v(3 5 32 +)   (virtual)
    1920x1200@60.000Hz 0.000kHz 0.00MHz  h(136 200 336 -)  v(3 6 36 +)   (virtual)
    2048x1536@60.000Hz 0.000kHz 0.00MHz  h(152 224 376 -)  v(3 4 49 +)   (virtual)
    2560x1440@60.000Hz 0.000kHz 0.00MHz  h(192 272 464 -)  v(3 5 45 +)   (virtual)
    2560x1600@60.000Hz 0.000kHz 0.00MHz  h(192 280 472 -)  v(3 6 49 +)   (virtual)
    3840x2160@60.000Hz 0.000kHz 0.00MHz  h(312 424 736 -)  v(3 5 69 +)   (virtual)
    4096x2160@60.000Hz 0.000kHz 0.00MHz  h(8 32 40 +)  v(48 8 6 -)   (virtual)
    5120x2160@60.000Hz 0.000kHz 0.00MHz  h(8 32 40 +)  v(48 8 6 -)   (virtual)
    640x480@60.000Hz 0.000kHz 0.00MHz  h(16 96 48 -)  v(10 2 33 -)  
    3840x2160@59.999Hz 133.319kHz 522.61MHz  h(8 32 40 +)  v(1 8 53 -)   (preferred)
    2560x1440@60.000Hz 88.860kHz 234.59MHz  h(8 32 40 +)  v(1 8 32 -)  
    4096x2304@59.999Hz 142.198kHz 593.82MHz  h(8 32 40 +)  v(1 8 57 -)   (preferred)
    3200x1800@59.999Hz 111.119kHz 364.47MHz  h(8 32 40 +)  v(1 8 43 -)  
    2560x2880@60.000Hz 177.720kHz 469.18MHz  h(8 32 40 +)  v(1 8 73 -)  
 -> 5120x2880@60.000Hz 177.720kHz 938.36MHz  h(16 64 80 +)  v(1 8 73 -)   (preferred) (tiled)

dispext1:
    640x480@60.000Hz 0.000kHz 0.00MHz  h(16 64 80 -)  v(3 4 13 +)   (virtual)
    800x600@60.000Hz 0.000kHz 0.00MHz  h(32 80 112 -)  v(3 4 17 +)   (virtual)
    1024x768@60.000Hz 0.000kHz 0.00MHz  h(48 104 152 -)  v(3 4 23 +)   (virtual)
    1280x720@60.000Hz 0.000kHz 0.00MHz  h(64 128 192 -)  v(3 5 20 +)   (virtual)
    1280x768@60.000Hz 0.000kHz 0.00MHz  h(64 128 192 -)  v(3 7 20 +)   (virtual)
    1280x1024@60.000Hz 0.000kHz 0.00MHz  h(80 136 216 -)  v(3 7 29 +)   (virtual)
    1400x1050@60.000Hz 0.000kHz 0.00MHz  h(88 144 232 -)  v(3 4 32 +)   (virtual)
    1680x1050@60.000Hz 0.000kHz 0.00MHz  h(104 176 280 -)  v(3 6 30 +)   (virtual)
    1600x1200@60.000Hz 0.000kHz 0.00MHz  h(112 168 280 -)  v(3 4 38 +)   (virtual)
    1920x1080@60.000Hz 0.000kHz 0.00MHz  h(128 200 328 -)  v(3 5 32 +)   (virtual)
    1920x1200@60.000Hz 0.000kHz 0.00MHz  h(136 200 336 -)  v(3 6 36 +)   (virtual)
    2048x1536@60.000Hz 0.000kHz 0.00MHz  h(152 224 376 -)  v(3 4 49 +)   (virtual)
    2560x1440@60.000Hz 0.000kHz 0.00MHz  h(192 272 464 -)  v(3 5 45 +)   (virtual)
    2560x1600@60.000Hz 0.000kHz 0.00MHz  h(192 280 472 -)  v(3 6 49 +)   (virtual)
    3840x2160@60.000Hz 0.000kHz 0.00MHz  h(312 424 736 -)  v(3 5 69 +)   (virtual)
    4096x2160@60.000Hz 0.000kHz 0.00MHz  h(8 32 40 +)  v(48 8 6 -)   (virtual)
    5120x2160@60.000Hz 0.000kHz 0.00MHz  h(8 32 40 +)  v(48 8 6 -)   (virtual)
    640x480@60.000Hz 0.000kHz 0.00MHz  h(16 96 48 -)  v(10 2 33 -)  
    3840x2160@59.999Hz 133.319kHz 522.61MHz  h(8 32 40 +)  v(1 8 53 -)   (preferred)
    2560x1440@60.000Hz 88.860kHz 234.59MHz  h(8 32 40 +)  v(1 8 32 -)  
    4096x2304@59.999Hz 142.198kHz 593.82MHz  h(8 32 40 +)  v(1 8 57 -)   (preferred)
    3200x1800@59.999Hz 111.119kHz 364.47MHz  h(8 32 40 +)  v(1 8 43 -)  
    2560x2880@60.000Hz 177.720kHz 469.18MHz  h(8 32 40 +)  v(1 8 73 -)  
 -> 5120x2880@60.000Hz 177.720kHz 938.36MHz  h(16 64 80 +)  v(1 8 73 -)   (preferred) (tiled)

dispext2:
    640x480@60.000Hz 0.000kHz 0.00MHz  h(16 64 80 -)  v(3 4 13 +)   (virtual)
    800x600@60.000Hz 0.000kHz 0.00MHz  h(32 80 112 -)  v(3 4 17 +)   (virtual)
    1024x768@60.000Hz 0.000kHz 0.00MHz  h(48 104 152 -)  v(3 4 23 +)   (virtual)
    1280x720@60.000Hz 0.000kHz 0.00MHz  h(64 128 192 -)  v(3 5 20 +)   (virtual)
    1280x768@60.000Hz 0.000kHz 0.00MHz  h(64 128 192 -)  v(3 7 20 +)   (virtual)
    1280x1024@60.000Hz 0.000kHz 0.00MHz  h(80 136 216 -)  v(3 7 29 +)   (virtual)
    1400x1050@60.000Hz 0.000kHz 0.00MHz  h(88 144 232 -)  v(3 4 32 +)   (virtual)
    1680x1050@60.000Hz 0.000kHz 0.00MHz  h(104 176 280 -)  v(3 6 30 +)   (virtual)
    1600x1200@60.000Hz 0.000kHz 0.00MHz  h(112 168 280 -)  v(3 4 38 +)   (virtual)
    1920x1080@60.000Hz 0.000kHz 0.00MHz  h(128 200 328 -)  v(3 5 32 +)   (virtual)
    1920x1200@60.000Hz 0.000kHz 0.00MHz  h(136 200 336 -)  v(3 6 36 +)   (virtual)
    2048x1536@60.000Hz 0.000kHz 0.00MHz  h(152 224 376 -)  v(3 4 49 +)   (virtual)
    2560x1440@60.000Hz 0.000kHz 0.00MHz  h(192 272 464 -)  v(3 5 45 +)   (virtual)
    2560x1600@60.000Hz 0.000kHz 0.00MHz  h(192 280 472 -)  v(3 6 49 +)   (virtual)
    3840x2160@60.000Hz 0.000kHz 0.00MHz  h(312 424 736 -)  v(3 5 69 +)   (virtual)
    4096x2160@60.000Hz 0.000kHz 0.00MHz  h(8 32 40 +)  v(48 8 6 -)   (virtual)
    5120x2160@60.000Hz 0.000kHz 0.00MHz  h(8 32 40 +)  v(48 8 6 -)   (virtual)
    640x480@60.000Hz 0.000kHz 0.00MHz  h(16 96 48 -)  v(10 2 33 -)  
    3840x2160@59.999Hz 133.319kHz 522.61MHz  h(8 32 40 +)  v(1 8 53 -)   (preferred)
    2560x1440@60.000Hz 88.860kHz 234.59MHz  h(8 32 40 +)  v(1 8 32 -)  
    3200x1800@59.999Hz 111.119kHz 364.47MHz  h(8 32 40 +)  v(1 8 43 -)  
    2560x2880@59.999Hz 177.718kHz 497.61MHz  h(8 32 200 +)  v(1 8 73 -)  
 -> 5120x2880@59.999Hz 177.718kHz 995.22MHz  h(16 64 400 +)  v(1 8 73 -)   (preferred) (tiled)

dispext3:
    720x480@59.940Hz 31.469kHz 27.00MHz  h(16 62 60 -)  v(9 6 30 -)   (overscan) (virtual)
    720x480@60.000Hz 31.500kHz 27.03MHz  h(16 62 60 -)  v(9 6 30 -)   (overscan) (virtual)
    1280x720@59.940Hz 44.955kHz 74.18MHz  h(110 40 220 +)  v(5 5 20 +)   (overscan) (virtual)
    1280x720@60.000Hz 45.000kHz 74.25MHz  h(110 40 220 +)  v(5 5 20 +)   (overscan) (virtual)
    720x576@50.000Hz 31.250kHz 27.00MHz  h(12 64 68 -)  v(5 5 39 -)   (overscan) (virtual)
    1280x720@50.000Hz 37.500kHz 74.25MHz  h(440 40 220 +)  v(5 5 20 +)   (overscan) (virtual)
    1920x1080@59.940Hz 67.433kHz 148.35MHz  h(88 44 148 +)  v(4 5 36 +)   (overscan) (virtual)
    1920x1080@60.000Hz 67.500kHz 148.50MHz  h(88 44 148 +)  v(4 5 36 +)   (overscan) (virtual)
    1920x1080@50.000Hz 56.250kHz 148.50MHz  h(528 44 148 +)  v(4 5 36 +)   (overscan) (virtual)
    3840x2160@23.976Hz 53.946kHz 296.70MHz  h(1276 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@24.000Hz 54.000kHz 297.00MHz  h(1276 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@25.000Hz 56.250kHz 297.00MHz  h(1056 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@29.970Hz 67.433kHz 296.70MHz  h(176 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@30.000Hz 67.500kHz 297.00MHz  h(176 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@50.000Hz 112.500kHz 594.00MHz  h(1056 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@59.940Hz 134.865kHz 593.41MHz  h(176 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    3840x2160@60.000Hz 135.000kHz 594.00MHz  h(176 88 296 +)  v(8 10 72 +)   (overscan) (virtual)
    800x600@60.000Hz 0.000kHz 0.00MHz  h(40 128 88 +)  v(1 4 23 +)  
    640x480@75.000Hz 0.000kHz 0.00MHz  h(16 64 120 -)  v(1 3 16 -)  
    640x480@60.000Hz 31.500kHz 25.20MHz  h(16 96 48 -)  v(10 2 33 -)  
    1280x1024@75.000Hz 0.000kHz 0.00MHz  h(16 144 248 +)  v(1 3 38 +)  
    1024x768@75.000Hz 0.000kHz 0.00MHz  h(16 96 176 +)  v(1 3 28 +)  
    1024x768@60.000Hz 0.000kHz 0.00MHz  h(24 136 160 -)  v(3 6 29 -)  
    800x600@75.000Hz 0.000kHz 0.00MHz  h(16 80 160 +)  v(1 3 21 +)  
    1152x864@75.000Hz 0.000kHz 0.00MHz  h(64 128 256 +)  v(1 3 32 +)  
    1280x1024@60.000Hz 0.000kHz 0.00MHz  h(48 112 248 +)  v(1 3 38 +)  
    1600x900@60.000Hz 0.000kHz 0.00MHz  h(24 80 96 +)  v(1 3 96 +)  
    1600x1200@60.000Hz 0.000kHz 0.00MHz  h(64 192 304 +)  v(1 3 46 +)  
    1920x1080@60.000Hz 67.500kHz 148.50MHz  h(88 44 148 +)  v(4 5 36 +)   (overscan) (preferred)
    3840x2160@29.970Hz 67.433kHz 296.70MHz  h(176 88 296 +)  v(8 10 72 +)   (overscan) (promoted)
    3840x2160@23.976Hz 53.946kHz 296.70MHz  h(1276 88 296 +)  v(8 10 72 +)   (overscan) (promoted)
    3840x2160@24.000Hz 54.000kHz 297.00MHz  h(1276 88 296 +)  v(8 10 72 +)   (overscan) (promoted)
    3840x2160@25.000Hz 56.250kHz 297.00MHz  h(1056 88 296 +)  v(8 10 72 +)   (overscan) (promoted)
 -> 3840x2160@30.000Hz 67.500kHz 297.00MHz  h(176 88 296 +)  v(8 10 72 +)   (overscan) (promoted)
    1920x1080@59.940Hz 67.433kHz 148.35MHz  h(88 44 148 +)  v(4 5 36 +)   (overscan) (preferred)
    1280x720@59.940Hz 44.955kHz 74.18MHz  h(110 40 220 +)  v(5 5 20 +)   (overscan) (promoted)
    1280x720@60.000Hz 45.000kHz 74.25MHz  h(110 40 220 +)  v(5 5 20 +)   (overscan) (promoted)
    720x480@59.940Hz 31.469kHz 27.00MHz  h(16 62 60 -)  v(9 6 30 -)   (overscan) (promoted)
    720x480@60.000Hz 31.500kHz 27.03MHz  h(16 62 60 -)  v(9 6 30 -)   (overscan) (promoted)
    640x480@59.940Hz 31.469kHz 25.17MHz  h(16 96 48 -)  v(10 2 33 -)  
    1920x1080@50.000Hz 56.250kHz 148.50MHz  h(528 44 148 +)  v(4 5 36 +)   (overscan) (promoted)
    720x576@50.000Hz 31.250kHz 27.00MHz  h(12 64 68 -)  v(5 5 39 -)   (overscan)
    1280x720@50.000Hz 37.500kHz 74.25MHz  h(440 40 220 +)  v(5 5 20 +)   (overscan)
    1920x1080@23.976Hz 26.973kHz 74.18MHz  h(638 44 148 +)  v(4 5 36 +)   (overscan) (promoted)
    1920x1080@24.000Hz 27.000kHz 74.25MHz  h(638 44 148 +)  v(4 5 36 +)   (overscan) (promoted)
    1920x1080@25.000Hz 28.125kHz 74.25MHz  h(528 44 148 +)  v(4 5 36 +)   (overscan) (promoted)
    1920x1080@29.970Hz 33.716kHz 74.18MHz  h(88 44 148 +)  v(4 5 36 +)   (overscan) (promoted)
    1920x1080@30.000Hz 33.750kHz 74.25MHz  h(88 44 148 +)  v(4 5 36 +)   (overscan) (promoted)
    2560x1440@59.951Hz 88.787kHz 241.50MHz  h(48 32 80 +)  v(3 5 33 -)  
perl -CSDA -Mutf8 -0777 "$scripts"/ioreg.pl < ioreg_m1max.24gpu.64gb.2tb.txt  387.52s user 0.92s system 99% cpu 6:28.93 total

 

[joevt]

It does appear that it's creating a second display port connection for each LG UltraFine 5K display (6 total + 1 for HDMI). All the LG UltraFine 5K displays are using a tiled mode.

In the ioreg output for the M1 Max:

I can see that there is support for four displays. The fourth display in this example is connected via HDMI. I wonder what it would look like if it was connected to Thunderbolt?

I can see there is 3 Thunderbolt buses, each with two Thunderbolt DisplayPort In Adapters. I can see the Thunderbolt controllers of the displays, each with two Thunderbolt DisplayPort Out Adapters.

What I can't see is the DisplayPort outputs from the GPU that connect to the DisplayPort In Adapters. There needs to be a way to detect the second DisplayPort connection of each LG UltraFine 5K display and get DPCD and EDID info, etc. The only indication that it's using two DisplayPort connections for a display is the fact that the current timing mode points to one that is tiled.

We know there's an internal display (disp0), and 4 external displays (dispext0 to dispext3). 3 of those can be dual link SST like the LG UltraFine 5K which means maybe there can be up to 7 external displays. Actually, Apple does have a IONameMatch for external displays dispext0 to dispext7 so they could be thinking about having 8 external displays in some future product.