M1 Mac Mini missing 4k@120Hz and DDC/CI support

[MLM]

I'm just piling on top of the mountain of issues people are having connecting various monitors to the M1 chip.

Connecting the M1 Mac Mini to an Acer XV273K display does not yield the 120 Hz option it should. Connecting the same monitor using the same cable to a 2019 15" Macbook Pro works just fine.

I should point out that it's not a bandwidth issue, as other have gotten it to work for different monitors: https://www.reddit.com/r/mac/comments/jvzvch
In addition there is no DDC/CI support, which makes it impossible to control the brightness of the monitor. This also works fine from the 2019 15" Macbook Pro using the same cable.

 

[joevt]

I'm just piling on top of the mountain of issues people are having connecting various monitors to the M1 chip.

Connecting the M1 Mac Mini to an Acer XV273K display does not yield the 120 Hz option it should. Connecting the same monitor using the same cable to a 2019 15" Macbook Pro works just fine.

I should point out that it's not a bandwidth issue, as other have gotten it to work for different monitors: https://www.reddit.com/r/mac/comments/jvzvch
In addition there is no DDC/CI support, which makes it impossible to control the brightness of the monitor. This also works fine from the 2019 15" Macbook Pro using the same cable.

What app do you use for DDC/CI support?

My guess is they need to talk to a different device to do DDC/CI on the M1 Mac because the graphics system/drivers is different on the M1 Macs.

 

[MLM]

What app do you use for DDC/CI support?

My guess is they need to talk to a different device to do DDC/CI on the M1 Mac because the graphics system/drivers is different on the M1 Macs.

Yeah I noticed there were issues with ddcctl among other things. Hopefully this will get fixed unrelated to my specific monitor model.

 

[Boomhowler]

Yeah I'm getting the same issues with a MB-air and the XV273K. Up to 1440p144 works great, but after that only 60 Hz. Have tried two "8k60"-capable usb-c -> DisplayPort cables and neither give any other result.

When connecting it to the gaming pc with an Nvidia card, it gets 4k120 without a problem, using a DisplayPort -> DisplayPort cable.

 

[Krevnik]

What resolution do you drive the XV273K at? I’m wondering if trying to drive it at 1440p@2x exceeds some internal limits, since the frame buffer would be a 5K one, where it might be bugging out and assuming 5K >60Hz won’t work, despite the final output being 4K?

If you are running it at 1440p@2x?, what happens when dropping to 1080p@2x?

 

[joevt]

Yeah I'm getting the same issues with a MB-air and the XV273K. Up to 1440p144 works great, but after that only 60 Hz. Have tried two "8k60"-capable usb-c -> DisplayPort cables and neither give any other result.

When connecting it to the gaming pc with an Nvidia card, it gets 4k120 without a problem, using a DisplayPort -> DisplayPort cable.

With the XV273K 4K120 might not work in some situations. 118Hz works. If there's a MST Hub then maybe 115Hz. But M1 Macs don't have a known method to add custom timings. 4K144 requires dual cable input but macOS has bad support for that (only works with displays that Apple tests).

 

[86Dylan86]

It’s also probably not displaying in RGB colour format as mentioned in other posts most if not all displays are stuck YPBPR a big issue yet to be fixed by apple, most people don’t realize the loss of image quality but if you go into your settings on your monitor it will most likely indicate this.

 

[Boomhowler]

What resolution do you drive the XV273K at? I’m wondering if trying to drive it at 1440p@2x exceeds some internal limits, since the frame buffer would be a 5K one, where it might be bugging out and assuming 5K >60Hz won’t work, despite the final output being 4K?

If you are running it at 1440p@2x?, what happens when dropping to 1080p@2x?

1440p HiDPI and 1080p HiDPI runs without any problems at 60 Hz, but I have to go down to 720p HDPI (or 1440p low resolution) for it to work at 120 or 144 Hz.

 

[Boomhowler]

With the XV273K 4K120 might not work in some situations. 118Hz works. If there's a MST Hub then maybe 115Hz. But M1 Macs don't have a known method to add custom timings. 4K144 requires dual cable input but macOS has bad support for that (only works with displays that Apple tests).

Why is that, if the XB273K works in 4K120?

 

[Krevnik]

1440p HiDPI and 1080p HiDPI runs without any problems at 60 Hz, but I have to go down to 720p HDPI (or 1440p low resolution) for it to work at 120 or 144 Hz.

That’s bizarre. About the only way that makes sense is if it’s somehow negotiating HBR2 speeds instead of HBR3, creating the limits you see... Unless at 720p HiDPI it’s 720p@3x. Very weird.

Why is that, if the XB273K works in 4K120?

DSC is supported by the XB273K, while the XV273K doesn’t. That makes the bandwidth limits easier to deal with. That said, I was pretty sure DisplayPort 1.4 should have no issues with 4K120 with 8bpc, and macOS doesn’t hide refresh rates that require 8bpc based on my testing.

But the other aspect is that the controllers between the two are different. So I wonder if there’s a quirk in the XV model that’s exposing a bug in the M1 DisplayPort handling.

 

[joevt]

Why is that, if the XB273K works in 4K120?

It depends on the GPU, driver, and pixel clock. I can do 118Hz 1078.06 MHz but not 119Hz 1088.06 MHz (CVT-RB timings).

You're correct - something is not quite right with my setup. I used "Restored factory settings" in SwitchResX to restore the default EDID of the DisplayPort connector of the display. This enabled the display's 3840x2160 119.88Hz 1065.51 MHz timing.

So it can do 120Hz if the pixel clock is less than 1080 MHz. DisplayPort 1.4 has a max of 1080 MHz for 8 bpc 4:4:4 RGB.

I connected a 4 lane DisplayPort 1.4 MST Hub. macOS accepts the 118Hz 1078.06 MHz timing but it won't work through the MST Hub. The MST Hub can pass the 120Hz 1065.51 MHz timing and a 117Hz 1068.31 MHz timing. So maybe with the MST Hub the max is reduced by 10 MHz (I didn't try to find the exact limit).

My 4 lane 3 port DisplayPort 1.4 MST Hub is supposed to support DSC, but AGDCDiagnose is not showing support. https://www.delock.com/produkt/87737/pdf.html?sprache=en
Maybe it needs a firmware update or maybe it only works in Windows or maybe it's an older version of DSC? Or maybe DSC is not supported when only one display is connected. I tried connecting two displays but that didn't change the DSC status.

The 2 lane 2 port DisplayPort 1.4 MST Hub of the CalDigit SOHO works correctly as I described previously or elsewhere.

 

[Boomhowler]

That’s bizarre. About the only way that makes sense is if it’s somehow negotiating HBR2 speeds instead of HBR3, creating the limits you see... Unless at 720p HiDPI it’s 720p@3x. Very weird.



DSC is supported by the XB273K, while the XV273K doesn’t. That makes the bandwidth limits easier to deal with. That said, I was pretty sure DisplayPort 1.4 should have no issues with 4K120 with 8bpc, and macOS doesn’t hide refresh rates that require 8bpc based on my testing.

But the other aspect is that the controllers between the two are different. So I wonder if there’s a quirk in the XV model that’s exposing a bug in the M1 DisplayPort handling.

The limits seems to almost coincide with the bandwidth limitations of HBR2 as you say.. Do you know of any way of checking in some display data or something which HBR-version that has been agreed on by display/computer?

It may be that @joevt is onto something here with the pixel clock being the culprit also. I am looking for data sheets for the XV273k and XB273k to see if the blanking % is different between them. Maybe Apple has used a pixel clock limit in the gpu that only allows for a certain amount of blanking (3840x2160x120 is only 995.3 M-pixels/sec) and that sweet spot is in between of what those two models use. But, I guess if the necessary pixel clock can't be above 1080 MHz anyway, because then it wouldn't work in windows as well (since it's outside of the standard)..

 

[Boomhowler]

or, I wonder if the case is that the connection tries to keep 10(30) bit/pixel since the options don't change when I enable HDR or not. 29.8 Gbps (4k120, 10bpp) is larger than the 25.92 limit of HBR3. But Apple removed the pixel depth information from System Report ... -> graphics and displays.. why?? I want to know what the display and the computer have agreed on.

Since the monitor and another computer works fine at 4k120 and the m1:s work fine with some other models, I would definitely blame some setup/handshaking procedure that is not working as it should/I expect it to do. I guess the xv273k is cheaper for a reason

 

[joevt]

But Apple removed the pixel depth information from System Report ... -> graphics and displays.. why??

It never showed the output pixel depth. What it did show is the frame buffer pixel depth which does not necessarily match the output pixel depth.

 

[Boomhowler]

It never showed the output pixel depth. What it did show is the frame buffer pixel depth which does not necessarily match the output pixel depth.

ah ok, didn't know that. Thanks

How can one find this information though? I guess the computer should very well know what it has handshaked with the display

 

[joevt]

How can one find this information though? I guess the computer should very well know what it has handshaked with the display

The AGDCDiagnose command can get the info for some Intel and AMD GPUs (for Intel Macs). Apple has a utility called cddebug not included with macOS to dump the info (it's used by sysdiagnose) - I believe most of the code used by cddebug is in CoreDisplay framework - so if we knew how sysdiagnose utilities worked (maybe by looking at utilities that are included), then cddebug could be recreated. I'm not sure if CoreDisplay is used by M1 Macs? For M1 Macs, if we can't find documented APIs to get the info, then I guess we would want to find the code that maintains the TimingElements and ColorElements properties in ioreg. Maybe the log show or log stream command can help find where to look.

 

[Krevnik]

or, I wonder if the case is that the connection tries to keep 10(30) bit/pixel since the options don't change when I enable HDR or not. 29.8 Gbps (4k120, 10bpp) is larger than the 25.92 limit of HBR3.

At least with my display, macOS displays refresh rates for both 10bpp and 8bpp supported modes. This is true for both my Intel MBP and M1 Mini.

For this to be true for this display, macOS would have to somehow ignore the 8bpp modes from the display’s EDID for some reason.

 

[Boomhowler]

At least with my display, macOS displays refresh rates for both 10bpp and 8bpp supported modes. This is true for both my Intel MBP and M1 Mini.

For this to be true for this display, macOS would have to somehow ignore the 8bpp modes from the display’s EDID for some reason.

ah ok, you see it in the display settings when choosing resolution/framerate?

 

[Krevnik]

ah ok, you see it in the display settings when choosing resolution/framerate?

Unfortunately no. How I know in my case is because of what the monitor supports. It supports 120Hz @ 10bpc, and 144Hz @ 8bpc because it is limited by DisplayPort 1.4, and doesn’t support DSC. So it’s impossible to drive the display at 144Hz @ 10bpc, yet macOS shows both 120Hz and 144Hz as options, and they both work.

 

[Boomhowler]

The AGDCDiagnose command can get the info for some Intel and AMD GPUs (for Intel Macs). Apple has a utility called cddebug not included with macOS to dump the info (it's used by sysdiagnose) - I believe most of the code used by cddebug is in CoreDisplay framework - so if we knew how sysdiagnose utilities worked (maybe by looking at utilities that are included), then cddebug could be recreated. I'm not sure if CoreDisplay is used by M1 Macs? For M1 Macs, if we can't find documented APIs to get the info, then I guess we would want to find the code that maintains the TimingElements and ColorElements properties in ioreg. Maybe the log show or log stream command can help find where to look.

Nice info, I'll see if I can do someting with it. It would be very interesting to see more what is happening "behind the scenes"when the display and computer handshakes capabilities.

 

[s_muxiu]

hello guys, I have updated my MacBook Air M1 to the last macOS Monterey beta version(21A5534d) few days ago and I can set my Display(xv273k) to 4k@120hz now!!!

See the Screenshot below:

 

[Boomhowler]

Great news! Hope they release Monterey quickly now so I can use it as well

 

[Pro Apple Silicon]

I'm anxious for these old threads to die away and new information to become available with the release of M1X products and macOS Monterey.

 

[Ronal]

I am on 11.6 big sur and I am running 4K @ 144hz with no problem with the M1.

 

[s_muxiu]

I am on 11.6 big sur and I am running 4K @ 144hz with no problem with the M1.

My Display (XV273k) doesn't support DSC feature and I can't set my Display up to 4K@120hz with my MBA M1 until this Monterey version (21A5534d).