- Mar 29, 2019
- Zbook G4 17
- Classic Mac
- Mobile Phone
There is no white list (only for secure Boot!!!!!!)I highly suspect a whitelist in the management engine, based on symptoms.
2 approved cards (4150,4170) only 2 roms post in discrete and both are present as part of the bios. And get shadowed from bios, not the card in discrete mode.
That means the source for the management engine's shadow rom has to be in the bios itself. This explains why Crane works in hybrid, but can't be shadowed and device-id or something else mismatches to what is allowed by management engine or simply management engine looks for rom in bios, can't find it and bricks on post.
One way to test this theory would be to change the id of a known working rom Aomorhid to match Crane and see it if posts.
Same but reverse would be to edit Crane's id to match Aomorhid, and see if it posts.
I suspect if done right the laptop will post but the management engine will use the bios version, completely ignoring the rom in the card.
Because the Bios itself has so many security redundancies, I don't think editing the bios would be a good solution, so we have to find a way to inject our rom from the card to acpi.
I dumped rom from VFCT table, but it was late night, so i cant remember how i did this.
The next step is to find where the image is located and to which one GFX0/*X* this one connected. I think, that if you change only one byte at this header (the number of spare, or subid device, then bios will no longer recognize gpu and will work only through MXM spi)
But!!! Only @nikey22 have suggestions about how to decode this data. Anyway the SMBus is connected to EC, and your firmware support any addresses of system management data, etc, so your system wont post about dead GPU as in my case. Why I am so sure?
That is really interesting why board have additional holes after SMD resistors, maybe this one connected else where, for example to chipset? And if i desolder those two resistors, maybe i will solve post issue problem? Hmm or somewhere else connected another device?
The other way, i started to test, but cant afford more time now to this way of efishell64 research. But recommend for reading: https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-30132232
By @joevt from macrummors