Is it possible to output 1920x1080 240Hz signal via HDMI or DP with the xrandr or something ?
1080p@240 Hz seems not verified before. Also, I am not what’s your question “xrandr” mean.
The mode on tegra must be from EDID of your monitor. You could not add arbitrary modes.
Is it possible to add arbitrary modes by myself ?
If yes, could you show me how to do it ?
The driver only accepts to use the form of EDID. So you need to first find a EDID that contains the mode you want.
Then, use the fallback method in below page to modify the kernel driver.
https://elinux.org/Jetson_TX2/r28_Display_debug -> * Forcing edid