usb: gadget: uvc: increase worker prio to WQ_HIGHPRI

This patch is changing the simple workqueue in the gadget driver to be
allocated as async_wq with a higher priority. The pump worker, that is
filling the usb requests, will have a higher priority and will not be
scheduled away so often while the video stream is handled. This will
lead to fewer streaming underruns.
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20220907215818.2670097-1-m.grzeschik@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_uvc.c

@@ -897,10 +897,14 @@ static void uvc_function_unbind(struct usb_configuration *c,
 {
 	struct usb_composite_dev *cdev = c->cdev;
 	struct uvc_device *uvc = to_uvc(f);
+	struct uvc_video *video = &uvc->video;
 	long wait_ret = 1;
 
 	uvcg_info(f, "%s()\n", __func__);
 
+	if (video->async_wq)
+		destroy_workqueue(video->async_wq);
+
 	/*
 	 * If we know we're connected via v4l2, then there should be a cleanup
 	 * of the device from userspace either via UVC_EVENT_DISCONNECT or

drivers/usb/gadget/function/uvc.h

@@ -88,6 +88,7 @@ struct uvc_video {
 	struct usb_ep *ep;
 
 	struct work_struct pump;
+	struct workqueue_struct *async_wq;
 
 	/* Frame parameters */
 	u8 bpp;

drivers/usb/gadget/function/uvc_v4l2.c

@@ -170,7 +170,7 @@ uvc_v4l2_qbuf(struct file *file, void *fh, struct v4l2_buffer *b)
 		return ret;
 
 	if (uvc->state == UVC_STATE_STREAMING)
-		schedule_work(&video->pump);
+		queue_work(video->async_wq, &video->pump);
 
 	return ret;
 }

drivers/usb/gadget/function/uvc_video.c

@@ -277,7 +277,7 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
 	spin_unlock_irqrestore(&video->req_lock, flags);
 
 	if (uvc->state == UVC_STATE_STREAMING)
-		schedule_work(&video->pump);
+		queue_work(video->async_wq, &video->pump);
 }
 
 static int
@@ -485,7 +485,7 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
 
 	video->req_int_count = 0;
 
-	schedule_work(&video->pump);
+	queue_work(video->async_wq, &video->pump);
 
 	return ret;
 }
@@ -499,6 +499,11 @@ int uvcg_video_init(struct uvc_video *video, struct uvc_device *uvc)
 	spin_lock_init(&video->req_lock);
 	INIT_WORK(&video->pump, uvcg_video_pump);
 
+	/* Allocate a work queue for asynchronous video pump handler. */
+	video->async_wq = alloc_workqueue("uvcgadget", WQ_UNBOUND | WQ_HIGHPRI, 0);
+	if (!video->async_wq)
+		return -EINVAL;
+
 	video->uvc = uvc;
 	video->fcc = V4L2_PIX_FMT_YUYV;
 	video->bpp = 16;