MP 1,1-5,1 4K Display on MP 5,1 with R9 280x

[Taipan]

Hi!
I need a new display for my old Mac Pro (4,1>) 5,1, and I‘m thinking about going 4k. Now I just read that there are some boot issues with these old machines and DP 1.2. But I haven‘t quite understood how severe they are going to. Can someone please distill this down for me?
My graphics card is a PowerColor R9 280x flashed with Mac ROM. My understanding is that I can drive a 4K display @ 60Hz on the DP port, but that‘s going to give me trouble with booting - unless, so I have read, I‘m using a second display connected to the card.
Since I have three displays connected, will I be fine? And can I drive the display with 1920x1080 (HiDPI) while still using the other displays at low DPI? Do I need third party software to set resolutions?
I‘m using OCLP with Monterey, in case that matters.

Thanks in advance!

 

[h9826790]

Hi!
I need a new display for my old Mac Pro (4,1>) 5,1, and I‘m thinking about going 4k. Now I just read that there are some boot issues with these old machines and DP 1.2. But I haven‘t quite understood how severe they are going to. Can someone please distill this down for me?
My graphics card is a PowerColor R9 280x flashed with Mac ROM. My understanding is that I can drive a 4K display @ 60Hz on the DP port, but that‘s going to give me trouble with booting - unless, so I have read, I‘m using a second display connected to the card.
Since I have three displays connected, will I be fine? And can I drive the display with 1920x1080 (HiDPI) while still using the other displays at low DPI? Do I need third party software to set resolutions?
I‘m using OCLP with Monterey, in case that matters.

Thanks in advance!

I can quite remember if "any DP 1.2 connection will makes the flashed 280X no boot", or "only the monitor that show the boot screen matters"

Anyway, the problem is that for flashed 280X, the Mac EFI UGA does not compatible with DP 1.2. Therefore, if the monitor set to DP 1.2 (this is required for 4K 60Hz), then the Mac EFI UGA stuck during boot, and the whole cMP stuck.

I don't think you can control which monitor to display the boot screen, but let's say if after all three monitors are connected, and the boot screen can show up via DVI. Then most likely you are good to go.

Beside, if you don't really need boot screen everyday, you may simply boot from the original non Mac EFI ROM. So that your setup guarantee can boot even a DP 1.2 monitor is connected. Only on the day that you really need boot screen, then boot from the Mac EFI ROM (many 280X has dual ROM, which allow you to do this simply by flipping a switch).

And the most advance (and permanent) option should be re-flash your card again with a UEFI GOP ROM, and also flash your cMP with EnableGOP. Then your setup will able to display boot screen even via DP 1.2 connection.

 

[Taipan]

Thanks for the reply!
That would have been my next question, if there‘s a way to select a specific display for the boot screen.
I didn‘t know about EnableGOP, sounds very interesting. Not sure whether I have the guts, though…
I haven‘t messed with the second ROM on the card, so it should still contain the GOP UEFI ROM, I guess. Can I safely try that by switching to it, then booting, and it should work as soon as the OS has loaded? Or will it already work when the OCLP boot picker is displayed?

 

[h9826790]

Thanks for the reply!
That would have been my next question, if there‘s a way to select a specific display for the boot screen.
I didn‘t know about EnableGOP, sounds very interesting. Not sure whether I have the guts, though…
I haven‘t messed with the second ROM on the card, so it should still contain the GOP UEFI ROM, I guess. Can I safely try that by switching to it, then booting, and it should work as soon as the OS has loaded? Or will it already work when the OCLP boot picker is displayed?

I don't think there is any way to control using which monitor to show boot screen.

EnableGop is publish for few months now. So far so good, I will say quite safe to try.

The other ROM on your card most likely has no GOP. At the time of 280X still manufacture, the ROM usually are just VBIOS. Some after market cards which release after GOP announced, the ROM may has UEFI, but that's very rare.

But you are safe to try the other ROM. You should still able to hear the POST "don", but the monitor will stay black until the GPU driver is loaded. Depends on your storage speed, that may take quite a bit of time. Just don't panic, let the computer do its job, then most likely you will be good.

For info, you can flip the switch after the cMP is powered up, but it won't do anything. So, if the cMP stuck in black screen, you can simply flip the switch back to the Mac EFI UGA position at anytime, even the cMP is running. But it won't has any effect until the next boot.

 

[Taipan]

OK, thanks again! Where can I get an UEFI GOP ROM for the card? Do I need Windows to flash it?
Edit: I think I have found a source (techpowerup.com) for ROMs as well as instructions for doing it myself).