Dell 5K display with 7950 GPU

[alphaod]

I have a Dell 5K display. I also got my old 2009 Mac Pro up and running again thanks some nice folks here. My Mac Pro is currently on High Sierra and it has the Sapphire 7950 Mac Edition graphics adapter. The computer runs fine.

So want to use my Dell 5K monitor with this computer, but it seems there is a problem. It will detect the display and it will boot to the desktop, but I can only choose 2560x1440 mirrored (so it will show the same desktop on "two" monitors of course I cannot see the other monitor as it's one display. The other option is I can set two 2560x2888 monitors, so now I've got two side-by-side tiles on the same monitor. Obviously the former is not ideal and the latter just looks ridiculous.

Any ideas?

 

[bookemdano]

I believe 5K requires two DP cables, doesn't it? Sorta like how 4K MST in the old days?

I could be very wrong, someone please correct me if so.

Edit: Maybe PM This guy and see if he ever found a solution? That's the only other post I found doing a quick search.

 

[alphaod]

Yes this particular 5K display uses two DisplayPort cables.

So I got myself the Sapphire RX 580 Pulse that comes with the Apple Developer eGPU kit (I literally removed it out of the eGPU I have). It boots in the Mac just fine , but it's the same issue. It seems I cannot get the Mac Pro to use the 5K display. The weird part is I can use the same graphics card in the eGPU box and my 15" MacBook Pro and my Mac Pro (2013) can both drive the 5K display using the same two cables through this particular card.

Which brings to be believe it's a software limitation. It doesn't seem a lot of people have this combination (seeing the Mac Pro precedes this monitor by many years). It's really bumming me out here.

 

[Pressure]

Please make a bug report directly to Apple and let us know if any solution pops up.

 

[alphaod]

Well based on my last couple hours of research, it would seem the best solution is that I get myself a Nvidia graphics card. It seems it is a driver issue and the AMD drivers do not recognize the Dell 5K display. That would make sense seeing both the MacBook Pro and the [2013] Mac Pro supports the display through the same graphics adapter.

I think I'll get myself a 1060 or something that uses a single power connector and see that is true.


As for reporting to Apple... I don't think they'll respond, except maybe they'll tell me I have an "vintage" product.

 

[alphaod]

I ended up getting a GTX 1060 which was actually worse. I don't know what happened, but when I plugged in my two DisplayPort cables, my monitor started to flicker like crazy. Even when I disconnected the cables, the monitor was still flickering. Fortunately Dell offers pretty good support and they told me I just needed to connect the monitor to a know good source and the voltage will stabilize and the flicker would be gone within the hour which turned out to be true.

I ended up moving my monitors around so my 5K display is running off my 2013 Mac Pro and the 2009 Mac with a GTX 1060 is running a 1440p display… I kept the 1060 because I found that the 7950 can't even drive a 1440p display over HDMI.