Jetson Xavier NX not displaying on some small monitors (RTD2660H)

[patzer0]

I own a Jetson Xaiver NX developer kit (8GB) running JetPack 5.1.3 (Ubuntu20.04), I found that there is no display on some small monitor modules with the same controller (RTD2660H), either 5inch or 7inch ones.
If I connect these monitors with Jetson, there would be no display after the very first boot screen (as the pic shows), even though Jetson boots normally (SSH is available).

The strange thing is, if Jetson boots with another regular PC monitor, there are no display problems, everything is fine. And if I switch the HDMI cable to the small monitor which cannot display before, it also functions well (as the pic shows).

Boot with the small monitor (display malfunction), xrandr output via NoMachine remote desktop:

jetson@ubuntu:~/Desktop$ xrandr
Screen 0: minimum 8 x 8, current 1024 x 600, maximum 32767 x 32767
HDMI-0 connected 1024x600+0+0 (normal left inverted right x axis y axis) 470mm x 260mm
   1024x600      59.82*+
   1920x1080     60.00    59.95    50.00  
   1280x1024     75.03  
   1280x720      60.00    59.94    50.00  
   1024x768      75.03    70.07    60.01  
   832x624       75.05  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   720x400       70.04  
   640x480       75.00    72.81    59.94  
DP-0 disconnected (normal left inverted right x axis y axis)

Everything seems just fine, but there is no display on the small monitor.

I’ve tried this small monitor with another Jetson of the same model with the same JetPack5.1.3 (freshly flashed) system, it still doesn’t work.
Given that my Jetson runs JetPack 5.1.3, would this be a problem of an old version of system? Or Jetson is just incompatible with this specific controller of monitor?

[linuxdev]

The driver for the integrated GPU (iGPU) differs from the discrete GPU (dGPU) drivers. HDMI is a “plug-n-play” system whereby a wire on the HDMI cable will query the monitor to ask for its specs. That data from the monitor, intersected with the modes the GPU driver supports, is what you have. The dGPU drivers (not compatible with Jetsons due to iGPU) can accept custom resolutions, whereas Jetsons can use only the modes from the query (which is the EDID data over the DDC wire). It is quite possible those small monitors do not have an accepted resolution/clock combination.

One think you can do is ask the driver itself what it thinks of all of those modes. The log file is found with “ls -ltr /var/log/Xorg.*.log | tail -n 1”. To get the explicit details of every mode you would need to first modify “/etc/Xorg/xorg.conf”. This is a plain text file, so open it with an editor (you’ll need sudo to save it), and look for:
Section "Device"

Within that you will add one line, so it will be similar to this excerpt:

Section "Device"
    Option "ModeDebug"
...snip...

Then reboot with your monitor. You can turn on logging on your serial console and log the content of that file (I’m assuming it is Xorg.0.log):
cat /var/log/Xorg.0.log
(then attach the serial console log; just turn on logging right before the cat command, then turn off logging)

What you’ll get is a mode pool, which is a list of all modes acceptable simultaneously to the driver and the monitor. My bet is that the monitors in question have no compatible modes, and so the mode pool would be empty.