Linux USB OTG: Difference between revisions
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= Configuring the USB OTG port under Linux = | = 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 | By default, the USB OTG port is configured as OTG in the device tree, and a USB type-C receptacle is assembled on the {{#var:HARDWARE_NAME}} custom board.<br> | ||
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.<br> | 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.<br> | ||
dr_mode: One of "host", "peripheral" or "otg". Defaults to "otg"<br> | dr_mode: One of "host", "peripheral" or "otg". Defaults to "otg"<br> | ||
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{{#ifeq: {{#var:HARDWARE_NAME}} | DART-MX8M | | {{#ifeq: {{#var:HARDWARE_NAME}} | DART-MX8M | | ||
<syntaxhighlight lang="diff"> | |||
&usb_dwc3_0 { | |||
status = "okay"; | |||
extcon = <&typec_ptn5150>; | |||
- dr_mode = "otg"; | |||
+ dr_mode = "host"; | |||
}; | |||
</syntaxhighlight> | |||
| | |||
{{#ifeq: {{#var:HARDWARE_NAME}} | DART-MX8M-PLUS | | |||
<syntaxhighlight lang="diff"> | <syntaxhighlight lang="diff"> | ||
&usb_dwc3_0 { | &usb_dwc3_0 { | ||
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}; | }; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
}} | }}}} | ||
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.<br> | 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.<br> | ||
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<pre> | <pre> | ||
# cat /sys/firmware/devicetree/base/usb@38100000/dwc3/dr_mode; echo | # cat /sys/firmware/devicetree/base/usb@38100000/dwc3/dr_mode; echo | ||
</pre> | |||
| | |||
{{#ifeq: {{#var:HARDWARE_NAME}} | DART-MX8M-PLUS | | |||
<pre> | |||
# cat /sys/firmware/devicetree/base/usb@32f10100/dwc3@38100000/dr_mode; echo | |||
</pre> | </pre> | ||
| | | | ||
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# cat /sys/firmware/devicetree/base/usb@32e40000/dr_mode; echo | # cat /sys/firmware/devicetree/base/usb@32e40000/dr_mode; echo | ||
</pre> | </pre> | ||
}} | }}}} | ||
= Using the USB OTG port under Linux = | = Using the USB OTG port under Linux = |
Revision as of 09:00, 16 November 2020
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 VAR-SOM-MX6 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-imx8mm-var-dart.dts
&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; echo
Using the USB OTG port under Linux
As host (default)
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.
Example using the g_mass_storage module to expose the root partition on eMMC to a PC while booting from recovery SD card:
Connect a type-C plug to Standard-A plug cable between the board and a PC, and run the following on the board:
# umount /dev/mmcblk0p1 # modprobe g_mass_storage file=/dev/mmcblk0p1
The partition should be loaded on the PC as a mass storage device.
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.