Broken firmware after High Sierra upgrade

[Beagl3]

Hi all,
after I had upgraded my 4.1->5.1 Mac Pro succesfully to High Sierra (including the firmware upgrade and the APFS conversion of my SM951), I ran into trouble rebooting from my macOS drive into my separate Windows SSD. One NVRAM reset later, the problem was fixed, but I noticed that my macOS drive didn't show up in the Bootcamp tool in Windows 10 anymore. Rebooting into macOS wasn't possible, so i tried to enter the startup manager by pressing alt while booting. This didn't work either. I tried removing every drive except my macOS one, but the Mac still booted into my non-existent Windows partition (but with a cryptic error message about missing boot disks). Any other key combination on boot like NVRAM reset, recovery mode or secure mode doesn't work either. When I press a key combination, the screen just goes white, flashes once and the Windows boot screen appears. Booting into Windows works fine, but anything else is completely broken. Has anyone an idea how to fix this?
Thanks a lot.

 

[h9826790]

Hi all,
after I had upgraded my 4.1->5.1 Mac Pro succesfully to High Sierra (including the firmware upgrade and the APFS conversion of my SM951), I ran into trouble rebooting from my macOS drive into my separate Windows SSD. One NVRAM reset later, the problem was fixed, but I noticed that my macOS drive didn't show up in the Bootcamp tool in Windows 10 anymore. Rebooting into macOS wasn't possible, so i tried to enter the startup manager by pressing alt while booting. This didn't work either. I tried removing every drive except my macOS one, but the Mac still booted into my non-existent Windows partition (but with a cryptic error message about missing boot disks). Any other key combination on boot like NVRAM reset, recovery mode or secure mode doesn't work either. When I press a key combination, the screen just goes white, flashes once and the Windows boot screen appears. Booting into Windows works fine, but anything else is completely broken. Has anyone an idea how to fix this?
Thanks a lot.

1) Your firmware is 100% normal, it is not broken. In fact, your whole case has nothing to do with the firmware.
2) What Windows can't read is the APFS partition. That's why it can't detect your High Sierra partition, and can't show up in the bootcamp control panel. If it's a HFS+ partition, bootcamp will work as expected.
3) Alt boot won't work because you are running a GTX970. Or you mean you are already running a flashed 970 but still doesn't work?
4) PRAM reset can make your Mac boot back to MacOS on the next boot, but it will break Nvidia web driver.
5) Pull out the Windows hard drive or can't use hot key to boot into recovery partition is "normal" when the target boot partition is pointed to a Windows drive.
6) again, nothing is broken, it's just you don't know what you did.

To fix it, the easiest way would be put a Mac EFI GPU back in. Then you can choose whatever boot partition you want during boot (alt boot).

If you can't use alt boot even with a Mac EFI GPU (e.g. you have keyboard issue), then I don't think PRAM rest can work as well. However, since you said that you can perform PRAM reset. So, the good news is PRAM reset is a guarantee fix for this issue. It will automatically point the target boot drive back to MacOS. However, in your case, you have to figure out how to re-activate Nvidia web driver.