MP 1,1-5,1 Mac Pro 5.1 won't boot with attached 4K Display

[F.A.D.]

Hello,

I replaced my two 23" Apple Cinema displays with a 43" LG 43UD79-B 4K Display which has very much the same PPI as my old displays which I like.

I'm using a 5.1 with the newest Firmware (144.0.0.0.0), a flashed Sapphire 7950 and a fresh Install of 10.14.5 on a PCIe NVME.

I have read many threads that a 4K display won't show a boot screen but that doesn't matter to me.

The really strange thing is that the computer will not boot when the display is attached!? It is attached via a Mini-Displayport to Displayport 1.2 cable. It runs just fine when I attach it when the computer has already booted. It also boots when I attach the 43" display and additionally one of my old 23" Displays (to either the second Mini-Display Port with an adapter or to the DVI Port).

I can disable the Displayport 1.2 function in the 43" display which will at least give me a boot screen that will get stuck when the apple logo shows up, it will stay there forever and not proceed the boot process. It will not start to show the progress bar under the logo.

Even when the display is shut down and disconnected from the power the MP will not boot as long as the cable is attached to the GPU which for me makes no sense at all.

I also did many PRAM resets as well as SMC resets etc.

I hope that someone way more clever than me has an answer to this problem.

Thank you all very much in advance for helping out!

Best regards!

Davd

 

[h9826790]

Set DP1.1 on the monitor side (stay with 4k 30Hz), or disconnect the DP cable until the cMP start to load the OS. 7950 Mac EFI UGA doesn’t support DP1.2 (or above).

It’s not just no boot screen, but won’t boot if you connect a DP1.2 display to a flashed 7950. It’s a known issue for a long time.

I don’t know why you can’t boot to desktop even with no display connected to the cables. Never heard this issue. But TBH, rather than find out what’s wrong. It’s so much easier to flash the original ROM back in, then you can boot the 7950 with whatever monitor connected. Boot screen won’t work anyway.

 

[F.A.D.]

Set DP1.1 on the monitor side (stay with 4k 30Hz), or disconnect the DP cable until the cMP start to load the OS. 7950 Mac EFI UGA doesn’t support DP1.2 (or above).

Or you can boot the 7950 with non Mac EFI ROM.

Thank you so much for your quick response!

The strange thing is when I'm switching to DP 1.1 on the monitor side it will show the Apple logo but will not proceed the boot process (it will not start to show the progress bar).

Are there any AMD cards (flashed) with Mac Efi that supports DP 1.2 for booting? I guess all the newer cards like 580X, Vega 56/64 and Radeon VII that will not show a boot screen anyway will work.

 

[tsialex]

Are there any AMD cards (flashed) with Mac Efi that supports DP 1.2 for booting? I guess all the newer cards like 580X, Vega 56/64 and Radeon VII that will not show a boot screen anyway will work.

None.

The most recent AMD card that can have pre-boot configuration support when installed in a MP5,1 is AMD R9-280X and it uses the same EFI from Sapphire AMD HD 7950 Mac Edition that don't support DP1.2.

 

[bookemdano]

Thank you so much for your quick response!

The strange thing is when I'm switching to DP 1.1 on the monitor side it will show the Apple logo but will not proceed the boot process (it will not start to show the progress bar).

Are there any AMD cards (flashed) with Mac Efi that supports DP 1.2 for booting? I guess all the newer cards like 580X, Vega 56/64 and Radeon VII that will not show a boot screen anyway will work.

If you don't care about having bootscreens (as you said in your OP) then you can use your 7950 just fine by moving its BIOS switch (google for info on location--it's tiny) to the other position. Unless both BIOSes on your card were flashed with the EFI firmware then the PC setting of the switch will result in you being able to boot with no problems on your 4K monitor.

This has been a longstanding issue. No perfect solution exists. You basically have to give up something.