usb: dwc3: gadget: Reduce TRB IOC settings

When the TRB ring is full, the dwc3 driver must make sure that there's
at least 1 TRB with Interrupt On Completion (IOC) set to notify of
available TRBs.

The current logic just sets the TRB's IOC whenever we run out of TRBs,
but it doesn't consider that there may be other TRBs with IOC/LST set
already. This creates more events and unnecessary delay from interrupt
handling. Only forcefully set IOC when we run out of TRBs and none of
the TRBs in the TRB ring has had IOC set.
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/72a1fa448eb1201b152e65be7902a5d1c75b9f3a.1667867687.git.Thinh.Nguyen@synopsys.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/gadget.c

@@ -1463,8 +1463,18 @@ static int dwc3_prepare_trbs_sg(struct dwc3_ep *dep,
 			 */
 			if (num_trbs_left == 1 || (needs_extra_trb &&
 					num_trbs_left <= 2 &&
-					sg_dma_len(sg_next(s)) >= length))
-				must_interrupt = true;
+					sg_dma_len(sg_next(s)) >= length)) {
+				struct dwc3_request *r;
+
+				/* Check if previous requests already set IOC */
+				list_for_each_entry(r, &dep->started_list, list) {
+					if (r != req && !r->request.no_interrupt)
+						break;
+
+					if (r == req)
+						must_interrupt = true;
+				}
+			}
 
 			dwc3_prepare_one_trb(dep, req, trb_length, 1, i, false,
 					must_interrupt);