Graphics Cards

[JaXXoN]

Hi!

Does the RX7900XTX support six FullHD displays when deploying DisplayPort multi-stream transport?

Background:

I currently use six 1680x1050 displays in a 3x2 configuration (three on top and three on the bottom) with the help of a Matrox TripleHead2Go Digital Edition where the upper three displays are connected to the TH2G - which in turn is connected to the DualLink-DVI output of a graphics card - and the lower three displays are connected to three DisplayPort outputs present on the same graphics card. Please note that the TH2G makes the three physical displays appear to be just on big display to the PC. Means, the PC detects only four displays, altogether.

As newer graphics card do not have DualLink-DVI outputs anymore, I need to look for another solution to get six displays working from the four output typically present on a consumer graphic card, i.e. 2x HDMI + 2x DP as present on many RX7900XTX cards.

Is it possible to connect the lower three displays to 2x HDMI + 1x DP outputs and the upper three displays to the second DP output deploying a Startech DP 1.4 MST splitter?

In case it is not possible to drive all four outputs of an RX7900XTX at the same time, is it possible to connect the upper three displays to the first DP output (via Startech MST) and the lower three displays to the second DP output (via a second Startech MST)?

Side note:

As an experiment, I purchased one Startech DP 1.4 MST splitter and connected the three upper displays to one DP output of an Nvidia GTX1070Ti (via the splitter) and then connected the three lower displays to the HDMI and the other two DP outputs. The six separate displays are recognized just fine, but it is not possible to use all six display at the same time as nvidia imposes a limit of four displays for consumer cards! In other words, I was just lucky that my setup worked so far because the TH2G makes three displays look as one and so the maximum number of displays was not exceeded. Does AMD has a similar restriction on the RX7900XTX?

Here's some more input in case somebody is curious: the Startech splitter works as expected, means, one DP output is split to three displays in "extended mode". I also tried to connected the TH2G to a DP output via a DP to DualLink-DVI adaptor. That works for 3840x1080 (2x 1920x1080) and 3840x1200 (2x 1920x1200), but not for 5040x1050 (3x 1680x1050) or 3360x1050 (2x 1680x1050). I assume I could upgrade to 3x2x 1920x1200 and then using two DP2DL-DVI adaptors and two TH2Gs to connect six 1920x1200 displays to four outputs (2x 3840x1200 via TH2G and DP2DVI adaptor and 2x 1920x1200 via plain HDMI), making the setup look as just four displays, but I think that's a little bit overkill ...

Feedback is highly appreciated!

TIA and best regards

JaXXoN

[JaXXoN]

Hi!

Answering my own posting: as far as I can tell, the RX 7900 XTX can only drive four displays!

To be more specific, the number of displays a video card can drive depends on the number of frame generators. With Linux, this information can be retrieved with the command "xrandr --listproviders". For my PowerColor RX 7900 XTX Red Devil, the output looks like this:

Provider 0: id: 0x57 cap: 0xf, Source Output, Sink Output, Source Offload, Sink Offload crtcs: 4 outputs: 4 associated providers: 1 name:AMD Radeon Graphics @ pci:0000:03:00.0

Here, the information "crtcs: 4" tells that a maximum of four displays can be driven, even when using MST.

I also purchased a RX 6950 XT for another PC and it shows "crtcs: 6". It can driver six displays: three displays connected directly to the video card and three more displays using a startech DP MST splitter. However, for me, it doesn't work reliable: after booting, only the three directly connected displays come up and for the other three displays I always need to reconnect the DP MST splitter on-the-fly - very annoying.

Anyway, for my six FullHD display setup, I ended up purchasing two "Matrox DualHead2Go Digital SE", which each split a DisplayPort into two FullHD DVI outputs. Means, two displays are directly connected to the video card and the other four are connected through the DH2G boxes. Works OOTB!

[JaXXoN]

BTW., I'm curious if the four display ("crtcs") limit is specific to my card or specific to the RX7900 chip itself. Serching for "crtcs: 6", it looks like all RX5700 and RX6700 (and up) can driver up to six display, but the RX7900 can only drive four.

I'd appreciate it if Linux users who deploy Radeon cards could post their output of "xrandr --listproviders".

I.e. the output for the IGPU on my ASUS ProArt X670E Creator is:

Provider 1: id: 0xab cap: 0xf, Source Output, Sink Output, Source Offload, Sink Offload crtcs: 4 outputs: 3 associated providers: 1 name:AMD Radeon Graphics @ pci:0000:6d:00.0

"outputs: 3" means it has three physical outputs (1x HDMI and 2x DP via USB4), but it can drive up to four displays ("crtcs: 4") using MST. I tested my six FHD display setup using the Startech DP MST adaptor and it works. It's even good enough for most of my use workstation cases

TIA and best regards