DisplayPort "dummy plug" not creating a desktop instance; HDMI is

I want to have a display emulated at the DisplayPort port, so that x11vnc can serve it for remote desktop access.

The approach works perfectly with an HDMI dummy plug.

However, when I connect a DP dummy plug, no desktop instance is created and thus no VNC desktop is served that I could connect to.

The DP dummy plug is recognized as a monitor in Windows, but in Jetson Linux
xrandr --listmonitors returns Monitors: 0

If I connect it to a real monitor, it retuns
Monitors: 1 0: +DP-0 2560/597x1440...

I do not understand why HDMI dummy plug works, but DP dummy plug not to achieve the same thing.

Can you help me identify the reason for this.

You can try to share the dmesg when you plug it into DP port and it will tell.

Plugging the DP dummy:

[13897.252567] tegradc 15210000.display: dp: plug event received
[13897.252674] hpd: state 3 (Disabled), hpd 1, pending_hpd_evt 1
[13897.252687] hpd: switching from state 3 (Disabled) to state 0 (Reset)
[13897.356191] hpd: state 0 (Reset), hpd 1, pending_hpd_evt 0
[13897.356217] tegradc 15210000.display: blank - powerdown
[13897.356262] extcon-disp-state external-connection:disp-state: cable 44 state 0 already set.
[13897.356269] Extcon DP: HPD disabled
[13897.356277] hpd: switching from state 0 (Reset) to state 1 (Check Plug)
[13897.356295] hpd: state 1 (Check Plug), hpd 1, pending_hpd_evt 0
[13897.356342] hpd: switching from state 1 (Check Plug) to state 2 (Check EDID)
[13897.358547] tegradc 15200000.display: unblank
[13897.358622] tegradc 15210000.display: blank - powerdown
[13897.364213] hpd: state 2 (Check EDID), hpd 1, pending_hpd_evt 0
[13897.364956] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 2
[13897.366506] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 1
[13897.368079] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 0
[13897.369640] tegradc 15210000.display: dp: aux write got error (0x10000100)
[13897.369913] tegradc 15210000.display: dp: Failed to write DPCD data. CMD 0x600, Status 0x10000100
[13897.370891] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 2
[13897.372416] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 1
[13897.373850] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 0
[13897.374793] tegradc 15210000.display: dp: aux write got error (0x10000100)
[13897.375059] tegradc 15210000.display: dp: Failed to write DPCD data. CMD 0x600, Status 0x10000100
[13897.375784] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 2
[13897.376730] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 1
[13897.377689] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 0
[13897.378622] tegradc 15210000.display: dp: aux write got error (0x10000100)
[13897.378829] tegradc 15210000.display: dp: Failed to write DPCD data. CMD 0x600, Status 0x10000100
[13897.379521] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 2
[13897.380822] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 1
[13897.381787] tegradc 15210000.display: dp: aux write retry (0x10000100) -- 0
[13897.383019] tegradc 15210000.display: dp: aux write got error (0x10000100)
[13897.383276] tegradc 15210000.display: dp: Failed to write DPCD data. CMD 0x600, Status 0x10000100
[13897.383617] tegradc 15210000.display: dp: failed to exit panel power save mode (0xfffffff2)
[13897.383880] hpd: edid read prepare failed
[13897.383892] tegradc 15210000.display: blank - powerdown
[13897.384067] extcon-disp-state external-connection:disp-state: cable 44 state 0 already set.
[13897.384073] Extcon DP: HPD disabled
[13897.384080] hpd: switching from state 2 (Check EDID) to state 3 (Disabled)
[13897.406886] tegradc 15200000.display: unblank
[13897.406915] tegradc 15210000.display: blank - powerdown

Plugging the HDMI dummy:

[14253.033595] extcon-disp-state external-connection:disp-state: cable 47 state 0
[14253.033632] Extcon AUX1(HDMI) disable
[14253.056610] tegra_nvdisp_handle_pd_disable: Powergated Head1 pd
[14253.057723] tegra_nvdisp_handle_pd_disable: Powergated Head0 pd
[14253.057852] tegradc 15200000.display: blank - powerdown
[14253.057971] extcon-disp-state external-connection:disp-state: cable 53 state 0
[14253.057978] Extcon HDMI: HPD disabled
[14253.057985] tegradc 15200000.display: hdmi: unplugged
[14253.063345] tegradc 15200000.display: blank - powerdown
[14253.063382] tegradc 15200000.display: unblank
[14253.063414] tegradc 15200000.display: unblank
[14253.063443] tegradc 15210000.display: blank - powerdown
[14253.165575] tegradc 15200000.display: blank - powerdown
[14253.165601] tegradc 15210000.display: blank - powerdown
[14253.714920] tegradc 15200000.display: blank - powerdown
[14253.715006] tegradc 15200000.display: unblank
[14253.716453] tegra_nvdisp_handle_pd_enable: Unpowergated Head0 pd
[14253.716678] tegra_nvdisp_handle_pd_enable: Unpowergated Head1 pd
[14253.724017] tegradc 15200000.display: hdmi: tmds rate:148500K prod-setting:prod_c_hdmi_111m_223m
[14253.725681] tegradc 15200000.display: hdmi: get YCC quant from EDID.
[14253.730021] extcon-disp-state external-connection:disp-state: cable 47 state 1
[14253.730028] Extcon AUX1(HDMI) enable
[14253.738584] extcon-disp-state external-connection:disp-state: cable 53 state 1
[14253.738598] Extcon HDMI: HPD enabled
[14253.738607] tegradc 15200000.display: hdmi: plugged
[14253.738800] tegradc 15200000.display: blank - powerdown
[14253.759511] extcon-disp-state external-connection:disp-state: cable 47 state 0
[14253.759519] Extcon AUX1(HDMI) disable
[14253.782218] tegra_nvdisp_handle_pd_disable: Powergated Head1 pd
[14253.783384] tegra_nvdisp_handle_pd_disable: Powergated Head0 pd
[14253.783513] tegradc 15210000.display: blank - powerdown
[14253.827443] tegradc 15200000.display: blank - powerdown
[14253.827494] tegradc 15200000.display: unblank
[14253.828834] tegra_nvdisp_handle_pd_enable: Unpowergated Head0 pd
[14253.829029] tegra_nvdisp_handle_pd_enable: Unpowergated Head1 pd
[14253.834409] tegradc 15200000.display: hdmi: tmds rate:148500K prod-setting:prod_c_hdmi_111m_223m
[14253.836018] tegradc 15200000.display: hdmi: get YCC quant from EDID.
[14253.840132] extcon-disp-state external-connection:disp-state: cable 47 state 1
[14253.840138] Extcon AUX1(HDMI) enable
[14253.840214] tegradc 15200000.display: unblank
[14253.840345] tegradc 15210000.display: blank - powerdown

Our dpaux pad just cannot communicate the EDID with this dummy connector. Which means cannot support.

Thanks!

Is there any chance to know which dummy connectors would be supported, other than ordering a few more and trying?

I tried downloading the EDID from the HDMI dummy, and writing it to the DP dummy, but that did not work out either.

Any tips how to proceed?

I never managed to get VNC connection working on any Jetson device, after following several guides. It always only shows Nvidia logo / splashscreen.

Only ever got it working using HDMI dummy plugs.

But this time, the AGX Orin custom carrier board only has DisplayPort.

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