<< Solved >> Sapphire Radeon HD 7750 Ultimate 1GB not fully working with Catalina 10.15.7

[watercoke]

I'm trying Catalina 10.15.7 using latest Lilu 1.5.1 + WhateverGreen 1.4.8 with radpg=15.
My GPU is Sapphire 7750 Ultimate 1GB (fanless) and I'm getting the following behaviour: HDMI works, DVI doesn't work (black screen / signal out of range), untested DP.

Boot flag -raddvi doesn't help to get DVI working neither, but according to WEG logging it's supposedly correcting the DVI digital transmitter for good.

With HDMI + DVI both connected, HDMI still works but some graphical glitches appears onscreen, and I can see DVI display correctly identified and active in IORegistryExplorer.

BTW, my card doesn't appear to have an UEFI rom: I don't get the "EFI Driver Version" on System Report -> Graphics/Displays, and GPU-Z on Windows agrees.
Maybe this could be an additional problem in my case, 'cause WEG FAQ states:

* What are the hardware requirements for WhateverGreen?
Full UEFI without CSM. You are strongly recommended to flash a UEFI-compatible ROM unless your card already has it. Failing to do so will quite likely result in issues in multi-monitor configurations and possibly even in single-monitor configurations. It may stil work for non-UEFI motherboards, try at your own risk. There are known issues when using 2 or more GPUs in multi-monitor configurations.

I've attached BIOS decoding output and WEG debug logs.

Any help will be greatly appreciated!

 

[watercoke]

Following up, I got it working

First I discovered that booting with HDMI display only connected (already working), then sleep -> wake, then hotpluging DVI / DP, everything worked ok (displays come alive).

So I reinforced the idea of a GPU re/initialization problem.

As suspected, the problem was indeed the non-UEFI support in GPU rom.
I added UEFI GOP (Graphics Output Protocol) to GPU rom using a tool by lordkag: GOPUpd_v1.9.6.5

The lordkag tool produced a binary identical (padding aside) rom to this one: https://www.techpowerup.com/vgabios/210668/210668
(just in case someone wanna try [no warranty, try at your own risk] and skip the dump+mod process for this same GPU brand/model)

Before modding, booting with CSM=disabled in GA-Z77-D3H bios automatically reverted back to CSM=enabled (with legacy support).
Now after modding the GPU rom with GOP UEFI support, the UEFI CSM in GA-Z77-D3H stays disabled during boot.

A new behaviour after modding is that only one screen display gets initialized during the AMI bios boot screen / bios setup in my HDMI+DVI connected setup, before mod both screens were on displaying this.
After initial AMI boot/post screen, everything stays like before, only HDMI displaying OpenCore boot, osx log, etc, but then UI comes alive in ALL SCREENS without sleep+wake trick, without gfx glitches, all good...

Sleep & wake still works ok with no problems like before. BTW, DP works but may still require some fine tunning / fixes, it's misbehaving sometimes while hotpluging it (switching monitor inputs, turn on / off display may get it working I believe <- I will not investigate this further as I don't plan to use DP anyway for now).

Finally, this eGPU only required CAIL_DisableGfxCGPowerGating=true, so no need for radpg=15 (which enables CAIL_DisableDrmdmaPowerGating, CAIL_DisableGfxCGPowerGating, CAIL_DisableUVDPowerGating and CAIL_DisableVCEPowerGating) to make it work.

 

[Asural]

As suspected, the problem was indeed the non-UEFI support in GPU rom.
I added UEFI GOP (Graphics Output Protocol) to GPU rom using a tool by lordkag: GOPUpd_v1.9.6.5

My HD7750 is now able to work with Opencore, thank you @watercoke.
I was surprised that it worked on Clober r5119 but not on Opencore.

I simply added UEFI to his VBIOS, so in my case I got a yellow screen without 'radpg = 15'.