[media] usbtv: discard redundant video fields

There are many dropped fields with some sources, leading to many
redundant fields without counterparts. When this redundant field
is odd, a new frame is pushed containing this odd field interleaved
with whatever was left in the buffer, causing video artifacts.

Do not push a new frame after processing every odd field, but do it
only after those which come after an even field.
Signed-off-by: Nikola Forró <nikola.forro@gmail.com>
Acked-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/usbtv/usbtv-video.c

@@ -312,8 +312,10 @@ static void usbtv_image_chunk(struct usbtv *usbtv, __be32 *chunk)
 	usbtv_chunk_to_vbuf(frame, &chunk[1], chunk_no, odd);
 	usbtv->chunks_done++;
 
+	/* Last chunk in a field */
+	if (chunk_no == usbtv->n_chunks-1) {
 		/* Last chunk in a frame, signalling an end */
-	if (odd && chunk_no == usbtv->n_chunks-1) {
+		if (odd && !usbtv->last_odd) {
 			int size = vb2_plane_size(&buf->vb.vb2_buf, 0);
 			enum vb2_buffer_state state = usbtv->chunks_done ==
 				usbtv->n_chunks ?
@@ -327,6 +329,8 @@ static void usbtv_image_chunk(struct usbtv *usbtv, __be32 *chunk)
 			vb2_buffer_done(&buf->vb.vb2_buf, state);
 			list_del(&buf->list);
 		}
+		usbtv->last_odd = odd;
+	}
 
 	spin_unlock_irqrestore(&usbtv->buflock, flags);
 }
@@ -639,6 +643,7 @@ static int usbtv_start_streaming(struct vb2_queue *vq, unsigned int count)
 	if (usbtv->udev == NULL)
 		return -ENODEV;
 
+	usbtv->last_odd = 1;
 	usbtv->sequence = 0;
 	return usbtv_start(usbtv);
 }

drivers/media/usb/usbtv/usbtv.h

@@ -95,6 +95,7 @@ struct usbtv {
 	int width, height;
 	int n_chunks;
 	int iso_size;
+	int last_odd;
 	unsigned int sequence;
 	struct urb *isoc_urbs[USBTV_ISOC_TRANSFERS];