Hello Sebastien,
We usually prefer to use the USB Composite Driver, not because of the i.MX, this is because the Host PC or any other device that you are planning to use, need to have the proper driver for the USB class that you want to use, in this case several options can be adopted, so the easy way to make sure the Host PC has the driver it is the common USB driver in this case the Composite one. Hope this clarify.
Have a great day,
Jaime
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