Use of USB port on GPU Expansion Module


What is the use case for the USB port built into the 7700 graphics module is it for DP over USB does it support power delivery. Couldn’t find anything in the Docs to give any further details.

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It’s only display-out, directly from the GPU. Plus USB 2.0.
There is no USB Power Delivery.


Ok I plugged it into my LG 34WK95U (5120x2160) via a usb-C → Display port cable. Windows detects it but the display is blank and lo -res.

Also tried plugging in the direct thunderbolt cable, same deal only it detects a low res monitor

If I connect the same monitor to the #1 USB 4.0 Port I get proper detection of the display using the same TB cable (although i have to plug it in the right way around)

Is this normal ?

I believe you can also plug in the hdmi or dp expansion cards into it and use a hdmi or dp cable to your display.

Yes but I doubt that is the intent though ?

It would be nice if they did a deep dive on that I don’t think they have yet ?

That the expansion cards work is kinda funny but certainly not the intended use.
Your port seems to have a problem and you might want to open a support ticket.

I’ve run into the same thing.

I have an LG 4K monitor with DP, HDMI, and USB-C inputs. I tried USB-C to USB-C with the output from the 7700S and got an image limited to 800 X 600. The resolution was greyed out, fixed at that resolution.

I have an HDMI expansion card that gets full resolution of my external monitor but that’s with the 780 graphics.

So unless I’m missing a setting or something, I’m also confused about the use case of the 7700S output from the dGPU.

Did anybody ever figure this one out? I used a USB-C cable from the FW16 to the monitor’s USB-C input. I was stuck on 800X600 resolution.

The use case is to connect a monitor, you’re supposed to get full resoltuion. Something is broken.
Did you know that not all USB C cables are created equal?
Maybe yours doesn’t have the bandwidth for DP Alt Mode

I think that is probably the problem. I’m going to pick up a new cable and see what happens.

As it is, I connected my HDMI module to the dGPU USC-C port and I get full resolution on the external display. So the GPU is working. I think you’re right, the cable was my limiting factor.

And the new 8k USB-C to HDMI cable works perfectly.


Just a minor update. on my progress using the port in the back of the 7700s

I managed to get the USB-C cable that came with my Dell monitor (provides power delivery and USB-C connection) to my MacBookPro to work with my LG 5k.

The dell cable supports Alternate mode with DP1.2, USB
3.1 upstream port ,Power Delivery PD up to 45W

This allowed the LG to display in 5k.

The thunderbolt cable that came with the LG would not work and only allowed 1024 x 720 and a blank screen, the monitor would complain of an incorrect DP version.

Nor did a USB-C to Display port cable work.


I’ve been using one of these for a couple of years with both my MacBook Pro and the work laptop : 4K USB C to DisplayPort adapter cable with break-proof metal connectors – 2m (supports 4K video/60Hz from notebooks/smartphones to large screens – DP, USB 3.1, Type C, Thunderbolt 3) by CableDirect: Computers & Accessories

Works fine with the FW16, when tested over the weekend on either the Expansion card USB-C ports or the dGPU port.

This is going to sound stupid - but did you try and reboot the laptop with the cable (that wasn’t working) plugged into the back?

I have a little adapter that I use - and when I first plugged it in, it wouldn’t allow me to activate the monitor (on Fedora).

After a reboot, my second display is up and running.

Just a thought in case someone else sees a similar issue.

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I have a dock and I tried connection to both USB C on side and the rear port on the graphics unit it will not activate my monitor. Any thoughts

I suspect the dGPU was off and didn’t wake up “from the plug in”. This is normal. You can wake it up by running lspci, nvtop, or reading sysfs files from it like sensor data. Then you wouldn’t need to reboot.


If it happens again, Ill have to try that - I had already been running games when I was trying the first time so maybe it had gone to idle.

I’d love to use the dGPU’s DP video out, but unsure if I need to buy a cable or if I can just plug my DP module into it?

I thought I’d try the module (got 2) and had some mixed success…

  • intermittently worked after a reboot, would not work if plugged in after booted up
  • by intermittently I mean SDDM would never launch driving both the laptop display and external monitor… post login would either bring a successful load with two displays, or would fail and dump be back to SDDM

With DP connected to the side (a second dp module), SDDM always loads with two screen (iGPU).

So either:

  • I should be able to use the DP module attached to the dGPU, but I have a bad one, or
  • I need to go buy a USB-C to DP cable to properly driver my monitor

You need to turn the dGPU on for the port to work after boot because the dGPU turns off when idle.
Open any GPU monitoring software (nvtop or mission center are examples), run lspci or read sysfs files for it.

Hi Mario,

I’m not sure I understand. Are you saying that whether I use the FW DP module or buy a USB-C to DP cable to connect a monitor to the dedicated dGPU USB-C port… the dGPU won’t care that it has a monitor plugged into it and go to sleep during the boot process so my external monitor will be blank before/during SDDM login (pre desktop)?

Why is the dGPU idle if I have a monitor connected to its dedicated display port? In my experience, a monitor connected to video card = you have work to do, show me an image, not go to sleep.

In a design where the only purpose for the dGPU is to be optionally used to drive the laptop panel instead of the iGPU… then sleeping the dGPU when not in use makes sense in an “on battery” use case (and not a bad option either for an “on AC, off battery” use case)… but the moment a dedicated port is added to the dGPU, the use case scenarios must be expanded:

Scenario #1 - On battery, external display on dGPU port, iGPU defaults to laptop panel
Monitor connected to dGPU port = stay awake. If I chose to keep the external monitor connected while on battery, then I accepted the expected increased power drain on the battery.

Scenario #2 - On AC, external display on dGPU port, iGPU defaults to laptop panel
If I am connected to AC (no battery drain)… why sleep the dGPU? If energy conservation is a concern, then they could always move the external monitor to one of the side DP/HDMI ports and that is covered by Scenario #4

Monitor connected to dGPU port = stay awake

Scenario #3 - On battery, dGPU port empty, iGPU defaults to laptop panel
Sleeping the dGPU makes sense here as there is no external monitor connected to the dGPU and the iGPU will driving the laptop panel.

If the user swaps in the dGPU to drive the laptop panel on battery, then they accept the expected increased power drain.

No monitor connected to dGPU port = sleep; until user wants panel/app driven by dGPU

Scenario #4 - On AC, dGPU port empty, iGPU defaults to laptop panel
Similar to Scenario #2… If I am connected to AC (no battery drain)… why sleep the dGPU? But like Scenario #3 there is no monitor connected on the dGPU port, so putting the dGPU to sleep is alright as the panel is driven by the iGPU, until the user chooses to swap the dGPU in to drive the laptop panel.

No monitor connected to dGPU port = sleep; until user wants panel/app driven by dGPU

Another Thought
I wonder why there isn’t a BIOS option to disable the iGPU in favor of the dGPU; thereby killing the sleep mechanism so it acts like a dedicated GPU.

Potential Work-a-rounds?
Is there a…

  1. kernel parameter I can add to GRUB,
  2. module I can add to mkintcpio/initramfs,
  3. conf file I can add to /etc/modprobe.d,
  4. or service i can add to systemd

…that will keep the dGPU awake if I have a monitor plugged to to directly? or if not, an override for the 5 second sleep entirely?