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I'm investigating why I can't connect a monitor to my PC's graphics card using an HDMI cable. I have my integrated graphics turned off in BIOS, and I typically use a DisplayPort with my monitor. If I recall correctly, the integrated HDMI port worked with the nouveau drivers before I changed over to using my graphics card exclusively.

  • Motherboard: Asus Z170-A. Relevant Ports: DP x 1, HDMI x 1
  • CPU: Intel i7-6700K
  • GPU: Nvidia GeForce GTX 1080. Ports: DP x 3, HDMI x 1 Nvidia Driver version: 384.111
  • LG 4K Monitor. Ports: DP x 2, HDMI x 1

Here's part of xrandr's output:

Screen 0: minimum 8 x 8, current 3840 x 2160, maximum 32767 x 32767
DVI-D-0 disconnected (normal left inverted right x axis y axis)
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
DP-4 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 600mm x 340mm 
DP-5 disconnected (normal left inverted right x axis y axis)

Firstly, why does xrandr report 6 DisplayPorts? Is it detecting the ones built in to my monitor, for daisy-chaining for instance?

Regardless, it clearly indicates that my working display connection is on DP-4. HDMI-0 and DP-0 must be my motherboard connections. My GPU HDMI port is in what would be the DP-2 position, which seems to indicate that my system is expecting a DisplayPort signal. Here's xrandr --verbose for that part:

DP-2 disconnected (normal left inverted right x axis y axis)
Identifier: 0x1c2
Timestamp:  2356520
Subpixel:   unknown
Clones:    
CRTCs:      0 1 2 3
Transform:  1.000000 0.000000 0.000000
            0.000000 1.000000 0.000000
            0.000000 0.000000 1.000000
           filter: 
CscMatrix: 65536 0 0 0 0 65536 0 0 0 0 65536 0 
BorderDimensions: 4 
    supported: 4
Border: 0 0 0 0 
    range: (0, 65535)
SignalFormat: DisplayPort 
    supported: DisplayPort
ConnectorType: DisplayPort 
ConnectorNumber: 2 
_ConnectorLocation: 2

Can I help my machine expect an HDMI signal in what is definitely a physical HDMI port? If this is a GPU firmware issue then I'll use a DisplayPort to HDMI adapter when connecting HDMI-only monitors.

  • xrandr is querying the GPU driver and showing logical ports -- these ports may not be wired to actual hardware ports. most likely the xrandr output only refers to the discrete GPU's ports -- the motherboard ports are attached to the integrated GPU built into your CPU. – quixotic Jan 20 '18 at 22:08
  • If it’s limited to my discrete GPU, why would there be 6 logical DisplayPorts? Further, why would there be only one HDMI port when I have two (unless you are correct that the integrated GPU is not displayed due to the queried driver in question; see first question)? Finally, why doesn’t the HDMI port detect a signal from a good cable and good monitor? Thank you for your reply. – soundssilver Jan 21 '18 at 0:36

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