New M1 HDMI issues in 11.3

[gaelenh]

Prior to 11.3, my Mac Mini M1 was having problems outputting HDMI to my capture card (Magewell 4K Plus LT). macOS wouldn't allow me to select 1080p resolution (only scaling to 1080 at 4k resolution) and it wouldn't allow me to change the refresh rate (stuck at 60hz instead of 120hz). My MacBook Pro 2015 worked as expected outputting over HDMI to my capture card and allowed me to select multiple resolutions and refresh rates, including my desired 1080p120.

It was a frustrating problem because the MBP and Mini M1 were doing different things and showing different display options under 11.2.x. After updating to 11.3, now neither work. +1 for consistency across devices!

My Mac Mini M1 shows "Unsupported Signal" outputting to my HDMI capture card. My MBP now also shows unsupported signal. The MBP laptop screen is also unusable, as it cycles through resolutions and switches on/off while its connected to the capture cards input.

Prior to 11.3 I was working with a ruby script posted elsewhere for a different HDMI issue (RGB settings) to override EDID data for the display. I didn't get to test this out fully because I upgraded to 11.3 hoping it would bring a fix. The only fix it brought was that now all my macs are consistently broken on the capture card.

Any ideas on how to fix or at the very least diagnose this?

 

[saynotosync]

I am not sure the EDID override ruby script was actually doing anything in your case, since that kind of EDID overrides is not supported on M1 Macs, from what I've seen.

 

[gaelenh]

I am not sure the EDID override ruby script was actually doing anything in your case, since that kind of EDID overrides is not supported on M1 Macs, from what I've seen.

Hmm. Do you know where EDID is being pulled from? Does macOS just use it straight from the device, or does macOS have it’s own built-in files/db with EDID? I can edit the EDID reported by the capture card with an edid formatter. It just seems suspicious that the display settings are broken on the old MBP and M1 after the 11.3 update.

 

[joevt]

EDID comes from the display - it's read by the GPU driver. The Apple display overrides may override some info in the EDID (at least display name on M1 Macs?) or most info in the EDID (for Intel Macs).

Some places in macOS (or most places for M1 Macs) may ignore the EDID override info. In that case, it would be nice to be able to patch the routine in the driver that does the EDID reading. That way it cannot be ignored - and you can do special stuff like make one display appear 100% as a different display with the OS having no clue that the display may be something else - and you could make the overrides per port instead of per display model so that two identical displays can be overridden differently depending on what GPU port it's connected to.

For example, Big Sur supports 5K width on Intel GPUs (Kaby Lake and Coffee Lake) but only if the real EDID contains a timing with a width that is greater than 4096 - a normal EDID override is not sufficient to enable 5K timings.

Another example, a normal EDID override cannot make two displays appear as a single dual tile display.

I haven't checked 11.3 to see if anything has changed.

 

[gaelenh]

EDID comes from the display - it's read by the GPU driver. The Apple display overrides may override some info in the EDID (at least display name on M1 Macs?) or most info in the EDID (for Intel Macs).

Some places in macOS (or most places for M1 Macs) may ignore the EDID override info. In that case, it would be nice to be able to patch the routine in the driver that does the EDID reading. That way it cannot be ignored - and you can do special stuff like make one display appear 100% as a different display with the OS having no clue that the display may be something else - and you could make the overrides per port instead of per display model so that two identical displays can be overridden differently depending on what GPU port it's connected to.

For example, Big Sur supports 5K width on Intel GPUs (Kaby Lake and Coffee Lake) but only if the real EDID contains a timing with a width that is greater than 4096 - a normal EDID override is not sufficient to enable 5K timings.

Another example, a normal EDID override cannot make two displays appear as a single dual tile display.

I haven't checked 11.3 to see if anything has changed.

Thanks for the info, joevt. Three days ago I didn't know what EDID data was, now I am editing it willy nilly. A new tech support achievement unlocked! I always wanted to know how os's knew what modes a monitor support.

In case anyone has this very specific problem or something related to it, I fixed it (?) by modifying the EDID data being reported by the Magewell capture card. I used Analog Way EDID editor (free download) to disable every established timing (res + refresh) in the default edid file exported from the capture cards preferences. I manually added modes for 1920x1080 at 120hz using the CVT wizard in the detailed data section and in the CEA extension. I then loaded the new EDID.

Now three modes are selectable: 1080p and 2 downscaled resolutions (1600x900, 1280x720). Most importantly, 120hz is selectable!

I question how fixed it is because during this process I noticed lots of significant color changes (notably green startup screen instead of black) which is probably related to non-RGB modes. I plugged HDMI's in different orders, restarted, and everything seems to look good, or at least passable now (seems somewhat saturated). Big Sur is doing some weird things with hdmi and/or display modes.

If I knew where macOS stored it's monitor info (like how it know when I plug in a monitor that I used last month to use the previous resolution and refresh rate), I could probably make headway into other people's reported 11.3 monitor issues. I wish I knew which EDID setting I made fixed it. My first pass where I added preferred modes didn't do anything, so I got heavyhanded and deleted every display mode except the one I wanted. There is probably a fix that has more finesse.

 

[joevt]

Thanks for the info, joevt. Three days ago I didn't know what EDID data was, now I am editing it willy nilly. A new tech support achievement unlocked! I always wanted to know how os's knew what modes a monitor support.

In case anyone has this very specific problem or something related to it, I fixed it (?) by modifying the EDID data being reported by the Magewell capture card. I used Analog Way EDID editor (free download) to disable every established timing (res + refresh) in the default edid file exported from the capture cards preferences. I manually added modes for 1920x1080 at 120hz using the CVT wizard in the detailed data section and in the CEA extension. I then loaded the new EDID.

Now three modes are selectable: 1080p and 2 downscaled resolutions (1600x900, 1280x720). Most importantly, 120hz is selectable!

I question how fixed it is because during this process I noticed lots of significant color changes (notably green startup screen instead of black) which is probably related to non-RGB modes. I plugged HDMI's in different orders, restarted, and everything seems to look good, or at least passable now (seems somewhat saturated). Big Sur is doing some weird things with hdmi and/or display modes.

If I knew where macOS stored it's monitor info (like how it know when I plug in a monitor that I used last month to use the previous resolution and refresh rate), I could probably make headway into other people's reported 11.3 monitor issues. I wish I knew which EDID setting I made fixed it. My first pass where I added preferred modes didn't do anything, so I got heavyhanded and deleted every display mode except the one I wanted. There is probably a fix that has more finesse.

Preferences are usually stored in plist files that can be modified by the defaults write command.
https://www.tonymacx86.com/threads/adding-using-hidpi-custom-resolutions.133254/post-2012632
https://forums.macrumors.com/thread...o-2-displayport-adapter.2270679/post-29339359
https://apple.stackexchange.com/que...fresh-rate-for-other-resolutions-less-than-4k

If you don't enter a full path for the preference file, then you access preferences in your user folder.
~/Library/Preferences