Five or six simultaneous displays with AMD GPU (eg 7970)?

[TheBloke]

Hi all

 

I currently use an NVidia 760 with four displays: 1 x 4K; 2 x 1920x1200; 1 x 1920x1080.   This mostly works, but I am considering replacing it with an AMD GPU - likely a Radeon 7970 - for two reasons:

1. I would like to add a fifth monitor, maybe even a sixth;
2. I get small stutters and slowdowns with my NVidia, using both Native and NVidiaWeb drivers.  It is a lot better than it was with my NVidia 980Ti, but it's still not perfectly smooth as it should be, especially when I have a full screen video playing while also doing UI movements like Swipe Left A Space or Mission Control.

 

I have just been told that it should be possible to access all display outputs on an AMD 79XX GPU, possibly requiring a custom SSDT and/or radeonDeInit?  I've only ever had one AMD GPU and that was 8 years ago so I am not experienced with them.  My NVidia 980Ti has five outputs, but can only use four at once.  But I believe AMD's EyeFinity does allow it to use them all as separate displays.

 

Before I buy the GPU, I'd be most grateful if anyone could confirm that it should be possible to run five or six simultaneous displays on a card such as the ASUS HD 7970 DirectCU II (6 x DP outputs) or XFX AMD Radeon HD 7970 (2 x mini-DP; 1 x HDMI; 2 x DVI).  With one display being 4K @ 60fps and the rest 1920x1200 or 1080P.

 

I have Googled on this a while but haven't yet found anyone discussing connecting more than four monitors to an AMD Hack  I did see that the late-2013 Mac Pro (which uses 2 x AMD FirePro GPUs) states it can support "up to 6 Thunderbolt displays".  So I know the OS can do it, it's just a question of whether a particular GPU can, and in a Hack setup.

 

Thanks very much

 

TB

[TheBloke]

I think I have this figured out now:

• Yes, AMD Eyefinity allows for a full six independent displays and it works on macOS
• Normally this is achieved using DisplayPort Multi-Stream Technology (MST), which involves hubs or adapters to split one DP port into multiple display connections
• But the Asus 7970 card I listed is able to support a full six connections without adapters.
• However, EyeFinity only allows for a maximum of two "legacy" connections.  Legacy means VGA, DVI or HDMI.
• Only two of my monitors support DP, so that means with my current screens I could only run four at once: 2 x DP + 1 x DVI + 1 x DVI -> HDMI.  Which is exactly what I already have.
• Using normal DisplayPort to HDMI/DVI cables or adapters would not help - this is still considered a DVI or HDMI connection, streamed within the DP protocol.
• However, there is an Active DisplayPort to HDMI adapter which converts DP to HDMI and is considered by the GPU to be true DP to DP .
• That adapter specifically states it works with EyeFinity, and that a maximum of two adapters can be used.
• Therefore, I could achieve six displays with the following configuration:
  • DP -> DP
  • DP -> DP
  • DVI -> DVI
  • DVI -> DVI
  • DP -> active adapter -> HDMI
  • DP -> active adapter -> HDMI
• In my case I would likely only use five displays, so I would only need one active adapter.  I do actually have a sixth screen, but it's another DVI.  There's also an active DP -> DVI adapter from a different manufacturer, but I really don't have room for six screens so I don't think I will need to go down that road   (If I did want to, it seems that I could use a standard HDMI to DVI passive cable/adapter plugged into the HDMI port.)

 

I am pretty sure that is all correct.   I'm sure enough to order a used Asus 7970, anyway. 

 

Of course it took me just long enough to work this out that the card I planned to Buy it Now on eBay has sold.  But that may not be the worst thing, because I've realised there's another Asus 7970 which is slightly faster, and there's one on auction that ends on Tuesday.   As well as another DirectCU II that ends Monday.

 

Thanks for listening

[TheBloke]

I'm just going to leave this here..

Seven displays baby.    Well, OK, six displays connected to the GPU.  And an iPad connected via Duet.  Still, seven!

This is achieved with the Asus Matrix 7970 3GB I mentioned earlier.  It's not yet perfect - after boot I only get a picture on two displays; the others have a signal and show up in Displays, but only show black.  The fix is to sleep and then wake.  Which only works with WhateverGreen installed, otherwise wake fails and I have to reboot.  But with WEG added I can sleep from the Login screen and immediately wake to get a picture on all screens, and then I'm good to go until reboot - including plugging/unplugging/swapping any connection/cable.

I don't plan to run with all seven displays.  The one on the far right I added just to check I could, and for purposes of the photo I will almost certainly lose that one, and go with 'just' the other five + iPad.  Also I need to move the TV on the left because I can only see 60% of it from where I sit; the rest is blocked by the two screens to its right.  I'm going to mount it a little higher and a little further away so I can see it all.

And finally I need to continue trying to fix the black-screen-after-boot issue.  I've spent many hours trying to patch a FrameBuffer, as per VladA's guide and using InjectATI=Yes in Clover.  No luck so far - all results are worse than what I get booting without any Clover graphical config at all.  But I will continue trying.  Or, an option I've yet to try is using a custom SSDT to try and achieve the same thing.

But I'm pretty happy that I can get the displays working at all, and even if I never solve the on-boot issue, having to sleep&wake after every reboot is certainly not the end of the world.

 

Edited March 12, 2018 by TheBloke

[LostVector]

very cool.  I have a FirePro W9000 connected to 3 Dell UP2715K's (2 DP cables per monitor).  On startup, getting all the monitors to sync up is somewhat random ... often, one screen will be blank.  I'm not sure what triggers this.  Less monitors connected seems to make the problem less bad, however.  I've been wondering if it's a signaling or voltage issue with all monitors connected.

 

WhateverGreen is, I think, more essential for proper operation than people realize.  It may seem like issues have gone away now with 10.13.4 and eGPU support, but I'm not convinced that is the case, based on all of the other fixes it seems to make.  Apple is really bad about hardcoding all the settings into the OS configuration ... often, improperly.

[Traace]

Just dont get a RX 480, I never managed to run quad display configuration with it, two of them always stay undetected (blackscreen) , even with WhatEverGreen.

 

It seems older cards like 7970 can handle it well.