DESK-MX8M-L/Peripherals/USB1 OTG

History
Version	Issue Date	Notes
1.0.0	Jan 2022	First DESK-MX8M release

Peripheral USB OTG

Device tree configuration

Here below an example of device tree configuration used on standard DAVE's kit for the ORCA SOM:

From imx8mp-mito8mplus-cb1001.dts:

&usb3_phy0 {
	vbus-power-supply = <&ptn5110>;
	fsl,phy-tx-vref-tune = <6>;
	fsl,phy-tx-rise-tune = <0>;
	fsl,phy-tx-preemp-amp-tune = <3>;
	fsl,phy-comp-dis-tune = <7>;
	fsl,pcs-tx-deemph-3p5db = <0x21>;
	fsl,phy-pcs-tx-swing-full = <0x7f>;
	status = "okay";
};

&usb3_0 {
	status = "okay";
};

&usb_dwc3_0 {
	dr_mode = "otg";
	hnp-disable;
	srp-disable;
	adp-disable;
	usb-role-switch;
	status = "okay";

	port {
		usb3_drd_sw: endpoint {
			remote-endpoint = <&typec_dr_sw>;
		};
	};
};

From carrier-common.dtsi:

Accessing the peripheral

Linux messages at boot time

...
...
[    4.954820] usb_otg_vbus: disabling
...
...

Usage with mass-storage

root@desk-mx8mp:~# dd if=/dev/zero of=mass_storage count=256 bs=1M
256+0 records in
256+0 records out
268435456 bytes (268 MB, 256 MiB) copied, 15.924 s, 16.9 MB/s
root@imx6qdlxelk:~# mkfs.msdos mass_storage
mkfs.fat 4.1 (2017-01-24)
root@desk-mx8mp:~# mkdir loop
root@desk-mx8mp:~# mount -o loop mass_storage loop
root@desk-mx8mp:~# echo "Test USB OTG with mass storage device" > loop/usb.txt
root@desk-mx8mp:~# umount loop

then insert the g_mass_storage kernel module driver enabling an Windows PC to see it as a removable device

root@desk-mx8mp:~# modprobe g_mass_storage removable=y file=mass_storage
[  891.807023] Mass Storage Function, version: 2009/09/11
[  891.813145] LUN: removable file: (no medium)
[  891.818901] LUN: removable file: /home/root/mass_storage
[  891.824754] Number of LUNs=1
[  891.827901] g_mass_storage gadget: Mass Storage Gadget, version: 2009/09/11
[  891.834955] g_mass_storage gadget: userspace failed to provide iSerialNumber
[  891.842109] g_mass_storage gadget: g_mass_storage ready
root@desk-mx8mp:~#

Once the USB cable is connected to the PC, the kernel prints the following messages:

root@desk-mx6:~# [  892.036840] g_mass_storage gadget: high-speed config #1: Linux File-Backed Storage

and the Windows PC activate the driver and the disk is available as a Drive Unit (with the usb.txt file available).

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