usb: device_next: limit CDC ACM OUT transfer size to the current MPS

When the controller is connected to a full speed bus, regardless of
whether the controller supports high speed or not, the transfer size for
the bulk OUT endpoint should be equal to the MPS in the current
configuration.

Signed-off-by: Johann Fischer <[email protected]>

Author: jfischer-no

subsys/usb/device_next/class/usbd_cdc_acm.c

@@ -596,6 +596,9 @@ static void cdc_acm_rx_fifo_handler(struct k_work *work)
 		return;
 	}
 
+	/* Shrink the buffer size if operating on a full speed bus */
+	buf->size = MIN(cdc_acm_get_bulk_mps(c_data), buf->size);
+
 	ret = usbd_ep_enqueue(c_data, buf);
 	if (ret) {
 		LOG_ERR("Failed to enqueue net_buf for 0x%02x", ep);