Black screen issue when enabling framebuffer-stolenmem (32MB DVMT locked in BIOS)

Hi everyone,

Not a first time hackintosher. I'm currently trying to hack a Surface Pro 6, i7-8650U, Intel UHD 620 with Catalina 10.15.6, with OpenCore 0.6.0. Whatevergreen, Lilu and VirtualSMC at their latest release (the ones from yesterday).

I'm having a bunch of issues with the DVMT being locked to 32M in the BIOS. There's no way to change that, so I have to work around it.

With the "Disable minStolenSize less or equal fStolenMemorySize assertion, 10.15.4 (based on Austere.J patch by PMheart)" kernel kext patch, I can correctly boot into 10.15.6, with accelerated GPU and correct scaling. Otherwise I get a Kernel Panic (expected, since 10.14.4, AFAIR)

Also I can only get acceleration spoofing the GPU as the HD620 (AAPL,ig-platform-id: 00001659, device-id: 16590000). Not sure if that's the way to go, if I don't specify neither ig-platform-id nor device-id, I get 0x3EA50009, which is a CFL framebuffer, and GPU acceleration isn't working. Kinda weird, but it seems that's what the UHD620 is (KBL CPU + CFL GPU, it seems).

The Whatevergreen docs advise to use device-id 16590000. Dortania also advises to use AAPL,ig-platform-id=0000C087, which gets me nowhere (does it need to be byte-swapped to something? I still don't know how and what needs to be byte-swapped).

Clearly, it isn't the way to go with Big Sur incoming. So I'm trying to get this thing to work using the "correct way" which is framebuffer patching.

If I do add the following stuff:

framebuffer-patch-enable Number 1

framebuffer-stolenmem Data 00003001

framebuffer-fbmem Data 00009000

I do not get a kernel panic, but it boots to a black screen. The GPU seems to be have been initialised correctly and the system to be booting, though. I just get nothing on screen.

I thought it might have something to do with connector patching, but if I use the kext patch, I do not need to specify any connector patches and it just works, not sure if that's expected?

I've also tried to use Hackintool to build a deviceProperty patch, but I still get a black screen.

Help please? This thing has had me stumped for weeks :(

submitted by /u/therealjbenam
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