WhateverGreen: Polaris AMD GPUs only send output to DisplayPort if Above 4G Decoding is not enabled/available

[Lost-Entrepreneur439]

I've gotten this result on a Sapphire Nitro+ RX 570 4GB and an MSI GAMING X RX 580 4GB, and on macOS Sierra, High Sierra, Catalina, Monterey and Ventura. I've also replicated this issue across four different motherboards, an MSI P55A-G55, MSI B360M BAZOOKA, ASRock Z370 Pro4, and an Acer Veriton M6618G.

If Above 4G Decoding is not enabled or available in the system's UEFI, macOS will only output to DisplayPort. HDMI and DVI just get a black screen. A lot of people still use older monitors without DisplayPort and older systems that lack the Above 4G Decoding option in the UEFI. I know people who are still running Core 2 Duos with Polaris cards, I myself am running a socket 1155 board which doesn't have this option with an RX 580.

I've tried the npci=0x2000 and npci=0x3000 bootargs, they did not fix the issue.

I haven't attached a Lilu or OpenCore log as I'm not sure if they're relevant to this issue, if one is wanted just let me know and I will attach it.

[Mieze]

You might want to try the to decode your UEFI setup module using UEFITool and ifrextract as described here: Disabling CFG Lock

This method was used to disable CFG-Lock on mainboards which lack the function in the setup GUI but can be applied to modify virtually any setup variable present on the system.

The UEFI usually includes many valuable functions which aren't exposed in the setup GUI but can be modified using setup_var with a modified GRUB shell. Maybe Above 4G Decoding is available in your UEFI and can be enabled that way?

[Lost-Entrepreneur439]

You might want to try the to decode your UEFI setup module using UEFITool and ifrextract as described here: Disabling CFG Lock

This method was used to disable CFG-Lock on mainboards which lack the function in the setup GUI but can be applied to modify virtually any setup variable present on the system.

The UEFI usually includes many valuable functions which aren't exposed in the setup GUI but can be modified using setup_var with a modified GRUB shell. Maybe Above 4G Decoding is available in your UEFI and can be enabled that way?

UEFITool can't open this computer's (the Acer Veriton) UEFI (error FfsParser::parse: not a single Volume Top File is found, the image may be corrupted across multiple images), likely due to this systems age, being one of those early UEFI systems where it must have CSM on.

One of the motherboards mentioned, specifically the P55A-G55, is a CSM only system and lacks UEFI at all.