RS232 is a protocol, but there are different implementations of physical voltage levels depending on hardware. The J21 serial console is specifically 3.3V (“TTL Level”). However, J21 won’t work for general purpose…this is wired as serial console. Each side will send garbage to the other as if they are users randomly typing into a keyboard at a logged in terminal.
For general communications you probably want to use J17. This is also 3.3V, but it isn’t configured as serial console. This connector does not require any additional driver beyond what the Jetson already has…the UART built in to the system provides this capability (this will show up as “/dev/ttyTHS2” on the Jetson). Had you chosen to plug in a cable which is a USB serial UART you would need that specific UART supported…the point is that the J17 and J21 serial UARTs already have drivers…external USB serial UARTs do not.
In the case of your device already having 3.3V serial UART wires your other device most likely already has its own driver as well. If the voltage level on your device is not 3.3V you will need to level shift it to 3.3V…1.8V won’t work, and 9-pin D-Sub connectors will cause damage. If your other device has this connector integrated I would not expect it to need an extra driver…if your other device is using a USB or other non-permanent removable serial port then it probably does need a driver.
Is your other device 3.3V? Is it integrated? Is it externally added, and if so, is it USB, PCI, so on?