Custom LVDS bringup in Xavier NX eDP

Autonomous Machines Jetson & Embedded Systems Jetson Xavier NX
1

Hi,

We are trying to bringup a custom LVDS display of resolution 1024x600 through eDP to LVDS bridge(PTN3460). We have generated the custom edid and replaced it in default_720p_edid[256]. But it is only affecting the HDMI output.

Both HDMI and DP edid values are replaced with our custom values. We verified the edid data with below command:
sudo cat /sys/kernel/debug/tegradc.X/mode

When checked using xrandr command the new resolution is reflected in HDMI, but it is not reflected in LVDS. We also got the below print with “xrandr” command:
xrandr: Output DP-0 is not disconnected but has no modes

I am attaching the display timings for reference:
1

Can anyone specify what needs to be done?

Note: When we used the standard values in default_720p_edid[256], both HDMI and DP edid data were same. But 720p was only reflected in HDMI and the LVDS was working on 640x480.

2

Do you see your expected EDID in:
sudo cat /sys/kernel/debug/tegradc.X/edid

I think in normal operation tegradc.0 is HDMI, and your eDP should be tegradc.1. The one with your EDID is the one which counts. There may be default modes or actively selected modes, but everything of interest starts with your EDID.

You might also consider attaching the boot log from serial console. For serial console, see:
https://www.jetsonhacks.com/2019/04/19/jetson-nano-serial-console/

You might also consider adding more logging regarding modes. If you go to “/etc/X11/”, and edit file “xorg.conf”, you will find a Section "Device". Update to include:

Section "Device"
...
   Option "ModeDebug"
...
EndSection

Depending on whether we are talking about “DISPLAY=:0” or “DISPLAY=:1” (I’ll pretend it is “:0”), then having that in the configuration extra mode information will be contained in the log file “/var/log/Xorg.0.log”. You could rename this with a “.txt” suffix and attach to the forums. The added logging will cause the driver to specifically say why it accepts or rejects every mode the EDID provides. Of course, if the earlier EDID shows no EDID was found, then the log won’t much matter.

4

Please disable HDMI in DTB and then dump the kernel log with DP only here.