usb: gadget: uvc: set nbuffers to minimum STREAMING_MIN_BUFFERS in uvc_queue_setup

We set the minimum amount of v4l2 buffers that is possibly be pending
to UVCG_STREAMING_MIN_BUFFERS which is two. This way the driver will
always have at least one frame pending to be encoded while the other
is being enqueued in the hardware.

Signed-off-by: Michael Grzeschik <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/uvc.h

···
 #define UVCG_REQ_MAX_INT_COUNT			16
 #define UVCG_REQ_MAX_ZERO_COUNT			(2 * UVCG_REQ_MAX_INT_COUNT)
 
+#define UVCG_STREAMING_MIN_BUFFERS		2
+
 /* ------------------------------------------------------------------------
  * Structures
  */

drivers/usb/gadget/function/uvc_queue.c

···
 #include <media/videobuf2-vmalloc.h>
 
 #include "uvc.h"
+#include "uvc_video.h"
 
 /* ------------------------------------------------------------------------
  * Video buffers queue management.
···
 
 	if (*nbuffers > UVC_MAX_VIDEO_BUFFERS)
 		*nbuffers = UVC_MAX_VIDEO_BUFFERS;
+	if (*nbuffers < UVCG_STREAMING_MIN_BUFFERS)
+		*nbuffers = UVCG_STREAMING_MIN_BUFFERS;
 
 	*nplanes = 1;