usb: dwc3: core: document struct dwc3_request

No functional changes. Merely adding useful
documentation for future readers.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/core.h

@@ -624,6 +624,19 @@ struct dwc3_hwparams {
 /* HWPARAMS7 */
 #define DWC3_RAM1_DEPTH(n)	((n) & 0xffff)
 
+/**
+ * struct dwc3_request - representation of a transfer request
+ * @request: struct usb_request to be transferred
+ * @list: a list_head used for request queueing
+ * @dep: struct dwc3_ep owning this request
+ * @first_trb_index: index to first trb used by this request
+ * @epnum: endpoint number to which this request refers
+ * @trb: pointer to struct dwc3_trb
+ * @trb_dma: DMA address of @trb
+ * @direction: IN or OUT direction flag
+ * @mapped: true when request has been dma-mapped
+ * @queued: true when request has been queued to HW
+ */
 struct dwc3_request {
 	struct usb_request	request;
 	struct list_head	list;