The downside is that the cdcacm struct requires a reference to the endpoint.

Why add a reference to the out endpoint ? I thought this endpoint could be accessible through usbus_interface_t field ?

Why add a reference to the out endpoint ? I thought this endpoint could be accessible through usbus_interface_t field ?

Good point, however, I think I need a proper getter for that first. Something along the lines of

usbus_endpoint_t *usbus_interface_find_endpoint(usb_ep_type_t type, usb_ep_dir_t dir);

Which would return a reference to the first endpoint matching the spec. This way we don't depend too much on the order the endpoints are added to the interface.

I think I need a proper getter for that first

I think this is the way to go, this is more generic and this may be reuse in another implementation later.

rebased to include the descriptor bug fix from #12535

And reordered the commits to keep stuff properly incremental

This looks good, please squash.

squashed!