usb: gadget: uvc: decrease the interrupt load to a quarter

With usb3 we handle many more requests. Decrease the interrupt load by
only enabling the interrupt every quarter of the allocated requests.
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

--
v1 -> v2: - edited patch description
	  - removed extra parantheses
	  - added a comment for the logic
	  - using unsigned int instead of int
	  - reinitializing req_int_count in uvcg_video_enable
v2 -> v3: -
Link: https://lore.kernel.org/r/20210628155311.16762-6-m.grzeschik@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/uvc.h

@@ -101,6 +101,8 @@ struct uvc_video {
 	struct list_head req_free;
 	spinlock_t req_lock;
 
+	unsigned int req_int_count;
+
 	void (*encode) (struct usb_request *req, struct uvc_video *video,
 			struct uvc_buffer *buf);
 

drivers/usb/gadget/function/uvc_video.c

@@ -360,6 +360,19 @@ static void uvcg_video_pump(struct work_struct *work)
 
 		video->encode(req, video, buf);
 
+		/* With usb3 we have more requests. This will decrease the
+		 * interrupt load to a quarter but also catches the corner
+		 * cases, which needs to be handled */
+		if (list_empty(&video->req_free) ||
+		    buf->state == UVC_BUF_STATE_DONE ||
+		    !(video->req_int_count %
+		       DIV_ROUND_UP(video->uvc_num_requests, 4))) {
+			video->req_int_count = 0;
+			req->no_interrupt = 0;
+		} else {
+			req->no_interrupt = 1;
+		}
+
 		/* Queue the USB request */
 		ret = uvcg_video_ep_queue(video, req);
 		spin_unlock_irqrestore(&queue->irqlock, flags);
@@ -368,6 +381,7 @@ static void uvcg_video_pump(struct work_struct *work)
 			uvcg_queue_cancel(queue, 0);
 			break;
 		}
+		video->req_int_count++;
 	}
 
 	spin_lock_irqsave(&video->req_lock, flags);
@@ -416,6 +430,8 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
 		video->encode = video->queue.use_sg ?
 			uvc_video_encode_isoc_sg : uvc_video_encode_isoc;
 
+	video->req_int_count = 0;
+
 	schedule_work(&video->pump);
 
 	return ret;