MP 1,1-5,1 RX580 and RX6800 simultaneously in MacPro5,1 - RX580 for Mojave / RX6800 for Monterey/Windows 10 possible?

[crackajacka77]

Hey there, I have a MacPro5,1 running OCLP 1.4.3 (OC 0.9.9) and switch between 10.14 Mojave for 32bit support, macOS 12 Monterey for newer apps and also Windows 10 for some occasional gaming.

Currently I have a RX580 installed in the MacPro5,1 but would like to put in a (already Mac flashed) RX6800 that I use in a dedicated PC (RX6800) for gaming currently. I have an external power supply available for powering both cards at the same time.

I'm running everything into a 30" Apple Cinema Display (Dual-DVI) and have the correct USB-C to Dual-DVI adapter which works fine with the screen and the other PC.

Is it possible to use the RX580 for Mojave and the RX6800 for Monterey and Windows? What configuration would be necessary for OpenCore to handle it?

Thanks!

Configuration:
MacPro5,1 (2010)
2x Xeon X5690 3,46 Ghz
96 GB 1333 RAM
1x PCI-E SATA III SSD running macOS 10.14 (and OpenCore)
1x SATA II SSD running macOS Monterey
1x SATA II SSD running Win10
1x Sapphire PULSE RX 580 8GB
1x AMD RX6800 Reference (Mac flashed)
30" Apple Cinema Display (Dual-DVI) + 24" HDMI screen

 

[crackajacka77]

Also, if it would be possible to port the RX6800 GPU support from Monterey into Mojave, then I wouldn't have these headaches from the beginning with

 

[tsialex]

First thing, how you gonna install it physically, the RX 6800 is a big GPU and not all models fit inside the MacPro5,1 case, requiring the PCIe fan to be moved. Two bigs GPUs will be very complicated to cool correctly inside a cramped MacPro5,1.

Second thing, Apple removed the possibility of using dissimilar GPUs with Mojave. Even without drivers for the RX 6800 with Mojave you will have weird problems. This does not work even with 2019 Mac Pro, people that install a RX6xxx GPU alongside the original Radeon 580X (the Apple name for the 2019 Mac Pro variant of the RX 580) have lot's of headaches/crashes - see the thread here - and then the solution is to remove the 580X.

If you get a way to install both cards without slow cooking the two GPUs overtime, you could try disabling the PCIe slot enumeration for the macOS you are booting, but this is too complex/cumbersome since you gonna need two OC configs.

You should get another MacPro5,1 dedicated to Mojave, will be easier/cheaper/a lot less headache.

 

[crackajacka77]

Hey tsialex, thanks for the answer - the RX6800 I already tested in the 5,1 (and thanks to this forum got it's VBIOS flashed) - works like a charm. Currently i'm using another dedicated PC for the RX6800, which of course is fine up until the point where you have to re-connect all the cables between the machines (Display/USB/LAN/FireWire), always quite the undertaking and not as seamless as one could wish. So, seems like ditching Mojave in the long-term is the way forward, unfortunately.

 

[Macschrauber]

I'd get a KVM Switch for the two machines and an Ethernet Switch for more Lan sockets.

It's not worth the effort and the risk to damage the box.

 

[crackajacka77]

Hey Macschrauber, also thanks for your dumper (did the GOP firmware patch today to 5,1).

I was thinking about that too, though dual monitor Dual-DVI capable KVM switches are quite the rare sight these days. Or in other words, I've never seen one capable of delivering 2560x1440 resolution for the 30" Apple Cinema Display.