WhateverGreen causes HP EliteDesk 800 RX560x to boot to black screen

[TonyC5]

When booting Sonoma and Sequoia on a Radeon RX560x-equipped HP EliteDesk 800 G4 / G5 Mini with Open Core 1.0.0, Lilu.kext 1.6.8 and WhateverGreen.kext 1.6.7, WhateverGreen automatically changes the default CFG_FB_LIMIT from 0 to 1. This change causes the RX560x with its single DP port to boot to black screen as diagnosed and solved in this thread. The "solution" is to override WhateverGreen's default automatic behavior by setting DeviceProperty CFG,CFG_FB_LIMIT=0.

The EFI (with debug log boot-args) used to diagnose this issue is attached here.

The Lilu/WEG debug logs that allowed this solution to be identified are attached here.

Proof of the solution is here.

IORegistry dumps that show CFG_FB_LIMIT test cases are here.

EDIT: Note that when I first created an Open Core EFI to test the HP EliteDesk 800 RX 560x, my OC config.plist included unnecessary ACPI > Patches GFX0->IGPU and PEGP->GFX0. This is because I was testing with and without WhateverGreen.kext. After initially posting this issue, I removed these unnecessary ACPI renames and I have confirmed that manually overriding CFG_FB_LIMIT is still required. The unnecessary renames did not affect WhateverGreen.kext in this case.

[TonyC5]

The black screen issue with this RX 560x can also be "fixed" by setting CFG,CFG_FB_LIMIT=2. More details are here.

[TonyC5]

Leaving the post below, but evidence here indicates that the EliteDesk 800 RX 560x dGPU card does not have a mobile RX 560x GPU. I thought that the Mobile GPU architecture might explain some of my observations and the WhateverGreen CFG_FB_LIMIT behavior, but now I'm not so sure.

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I wonder if this explains why this HP EliteDesk 800 G4 Mini RX 560x dGPU card does not behave as WhateverGreen expects it to behave: this RX 560x dGPU card is based on the RX 560x Mobile GPU. According to TechPowerUp, "This device has no display connectivity, as it is not designed to have monitors connected to it. Rather it is intended for use in laptop/notebooks and will use the output of the host mobile device. Radeon RX 560X Mobile is connected to the rest of the system using a PCI-Express 3.0 x16 interface."