From Variscite Wiki

1 Configuring the USB OTG port under Linux

By default, the USB OTG port is configured as OTG in the device tree, and a USB type-C receptacle is assembled on the DART-MX8M-MINI custom board.
To use it as host only or peripheral only you need to change the value of the dr_mode property under the USB node in the device tree.
dr_mode: One of "host", "peripheral" or "otg". Defaults to "otg"

For example:
Follow either the "Build the Linux kernel from source code" or "Customizing the Linux kernel" Wiki pages and edit the following device tree file:
arch/arm64/boot/dts/freescale/imx8mm-var-dart-customboard.dts for DART-MX8M-MINI, or arch/arm64/boot/dts/freescale/imx8mm-var-dart-customboard.dts for VAR-SOM-MX8M-MINI

&usbotg1 {
-	dr_mode = "otg";
+	dr_mode = "host";
	picophy,pre-emp-curr-control = <3>;
	picophy,dc-vol-level-adjust = <7>;
	status = "okay";

If you build the kernel manually from source code, you should build only the device trees and copy them to your SD card or eMMC.

Note: You can read the current dr_mode value on a running target, by executing the following command:

# cat /sys/firmware/devicetree/base/usb@32e40000/dr_mode;

2 Using the USB OTG port under Linux

2.1 As host (default)

USB host

2.2 As peripheral

In order to use the board as a peripheral, an appropriate module needs to be loaded.
For example, there is an Ethernet gadget module called g_ether, a mass storage gadget called g_mass_storage, a serial gadget called g_serial, etc.

2.2.1 Examples

Connect a type-C plug to Standard-A plug cable between the board and a host PC, and run the following examples on the target board: Mass Storage Device

The following uses the g_mass_storage module to expose the root partition on eMMC to a PC while booting from recovery SD card:

# umount /dev/mmcblk2p1
# modprobe g_mass_storage file=/dev/mmcblk2p1

The partition should be loaded on the PC as a mass storage device. USB Debug Console

The following uses the g_serial module to spawn a new debug console over USB:

On target:

# echo g_serial > /etc/modules-load.d/g_serial.conf       # Load g_serial module on boot
# sudo systemctl enable getty@ttyGS0.service              # Spawn a new tty session on ttyGS0
# reboot                                                  # Reboot to take effect

On Host:

$ minicom -D /dev/ttyACM0                                 # Launch minicom on Host computer to login to target tty console

2.3 As OTG

With OTG, the board can be either a host, or a peripheral.
In order to use it as a host and connect a peripheral (e.g. a USB flash drive) to it, either use a peripheral with type-C connector or use type-C to type-A adapter.
In order to use it as a peripheral and connect it to a PC, for example, a cable with a type-C plug on one end and a Standard-A plug on the other is needed.