How to install Windows 10 on Mac with A Flashed AMD Radeon HD7950 GPU

[h9826790]

Has it been determined why the 7950's EFI rom has trouble booting Windows in EFI mode, but other GPUs (Apple branded & Nvidia) don't?

Never see any info on this topic, all we know is just the 7950 Mac EFI cannot work with Windows EFI mode.

 

[HandsomePixel]

No, I couldn't figure that out at all. The only way I was able to install Windows 10 was changing the switch position to the opposite end (I am actually using the reference card), changing the EFI boot ROM used that is also compatible with Windows 10.
We now know what does NOT works now, so that's something

 

[MisterAndrew]

Hmm, yeah it’s kind of annoying. Since I Boot Camp I decided on a GTX 680 as my backup card instead of the HD 7950.

 

[startergo]

My experience shows that flashed R9 280X bios only works with the basic Microsoft display adapter (it says 2006 so don't expect too much from it) for the Windows EFI installs. Windows in legacy mode has no problem with the flashed bios.

 

[ZStech]

TL;DR How to install Windows 10 on Mac with Flashed AMD Radeon HD7950

Due to the sheer frustration this installation has been giving me, I caved and decided to ask if any of you can help me with this.

I am trying to install Windows 10 on my Mac Pro which was bought maxed out (2 quad core xeon processors, 32GB of RAM, plus a 480GB SSD as the Mac boot drive).
Fast forward a couple of years, and I decide to upgrade the GPU for video editing, and found the AMD Radeon HD 7950 (Not the Sapphire/Official version), which was flashed from the seller on eBay to have the boot screen functionality on Mac (the menu to choose what boot drive, recovery mode, etc.).

Now to the problem.
I burned the Windows 10 ISO to a DVD (couldn't boot AT ALL from "burning" the ISO to a usb stick).
After insterting/leaving the DVD disc inside, turning off the computer, turning it back on while holding ALT/Option key, and finally choosing the disc that says "EFI" (black screen as well when choosing "Windows"), the Windows 10 logo would appear for a couple of minutes and then an error would show saying "Your PC needs to be repaired".

What's mind-boggling for me is that I tried all of these exact steps on another Mac Pro that doesn't have an upgraded GPU, just the one it came with, and it worked! Windows installed on it and booted and everything!

I've come across a few threads about people having very similar issues where they upgrade the GPU (although all of them state that they were using the PC variant of the card without being flashed (losing the boot menu and other things every time they boot up their computer which I use))
From what I could understand from all of these threads is that the problem resides in Windows booting in EFI mode when their card doesn't support it?
I just want to run Windows for games, and that's it.
Too much trouble trying to use Wine or PlayOnMac while trying to install lots of libraries and such just to play some games (plus many more that aren't supported.)
Really appreciate it if someone could help.

BOOTCAMP is the only utility I recommend you to use. It's simple to work with and do not require many steps to perform the installation.

 

[sgtwicki]

I am also having that issue with my cMP 4,1 ->5,1. I still can't boot Windows with the Radeon BIOS switch in "Mac mode".
With the latest Windows updates and AMD drivers, Windows no longer crashes on boot like it used to, but now it just reboots over and over.
My EFI install of Windows 10 on an SSD in the optical bay boots fine with the Radeon BIOS switch in the other position. I'd rather not use BootCamp/BIOS mode, and lose the advantages of SATA/AHCI/NVMe.