Linux USB OTG

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DART-MX8M USB OTG

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 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/fsl-imx8mq-var-dart-common.dtsi

&usb_dwc3_0 {
	status = "okay";
	extcon = <&typec_ptn5150>;
-	dr_mode = "otg";
+	dr_mode = "host";
};

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@38100000/dwc3/dr_mode;

Using the USB OTG port under Linux

As host (default)

USB host

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.

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/mmcblk0p1
# modprobe g_mass_storage file=/dev/mmcblk0p1

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

Ethernet Device

The following uses the g_ether to establish an ethernet link with a host computer over USB.

First, connect a USB cable from a host computer to the USB OTG port of the target. Then run the following commands:

On the target:

Load the g_ether module, assigning the host mac address 02:00:00:00:00:01
Note: you may exclude the host_addr argument, it's used here because the host computer will rename usb0 to enx020000000001
# modprobe g_ether host_addr=02:00:00:00:00:01

Tell NetworkManager not to manage this interface (skip this step if NetworkManager is not running on the target)
# nmcli dev set usb0 managed no

Assign a static IP address of 192.168.10.2
# ip addr flush usb0; ip addr add 192.168.10.2/24 dev usb0; ip link set usb0 up

On the host computer:

Tell NetworkManager not to manage this interface (skip this step if NetworkManager is not running on the host)
# nmcli dev set enx020000000001 managed no

Assign a static IP address of 192.168.10.1
$ sudo ip addr flush enx020000000001; sudo ip addr add 192.168.10.1/24 dev enx020000000001; sudo ip link set enx020000000001 up

Ping the target from the host:

$ ping 192.168.10.2 -c 3
PING 192.168.10.2 (192.168.10.2) 56(84) bytes of data.
64 bytes from 192.168.10.2: icmp_seq=1 ttl=64 time=0.931 ms
64 bytes from 192.168.10.2: icmp_seq=2 ttl=64 time=0.822 ms
64 bytes from 192.168.10.2: icmp_seq=3 ttl=64 time=0.777 ms

--- 192.168.10.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2032ms
rtt min/avg/max/mdev = 0.777/0.843/0.931/0.064 ms

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.