2 files changed, 66 insertions, 17 deletions

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 14a360490be9..0d5b84f3b570 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -1378,6 +1378,39 @@ int vb2_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b)
 }
 EXPORT_SYMBOL_GPL(vb2_prepare_buf);
 
+/**
+ * vb2_start_streaming() - Attempt to start streaming.
+ * @q:          videobuf2 queue
+ *
+ * If there are not enough buffers, then retry_start_streaming is set to
+ * 1 and 0 is returned. The next time a buffer is queued and
+ * retry_start_streaming is 1, this function will be called again to
+ * retry starting the DMA engine.
+ */
+static int vb2_start_streaming(struct vb2_queue *q)
+{
+        int ret;
+
+        /* Tell the driver to start streaming */
+        ret = call_qop(q, start_streaming, q, atomic_read(&q->queued_count));
+
+        /*
+         * If there are not enough buffers queued to start streaming, then
+         * the start_streaming operation will return -ENOBUFS and you have to
+         * retry when the next buffer is queued.
+         */
+        if (ret == -ENOBUFS) {
+                dprintk(1, "qbuf: not enough buffers, retry when more buffers are queued.\n");
+                q->retry_start_streaming = 1;
+                return 0;
+        }
+        if (ret)
+                dprintk(1, "qbuf: driver refused to start streaming\n");
+        else
+                q->retry_start_streaming = 0;
+        return ret;
+}
+
 static int vb2_internal_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
 {
         int ret = vb2_queue_or_prepare_buf(q, b, "qbuf");
@@ -1426,6 +1459,12 @@ static int vb2_internal_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
         /* Fill buffer information for the userspace */
         __fill_v4l2_buffer(vb, b);
 
+        if (q->retry_start_streaming) {
+                ret = vb2_start_streaming(q);
+                if (ret)
+                        return ret;
+        }
+
         dprintk(1, "%s() of buffer %d succeeded\n", __func__, vb->v4l2_buf.index);
         return 0;
 }
@@ -1575,7 +1614,8 @@ int vb2_wait_for_all_buffers(struct vb2_queue *q)
                 return -EINVAL;
         }
 
-        wait_event(q->done_wq, !atomic_read(&q->queued_count));
+        if (!q->retry_start_streaming)
+                wait_event(q->done_wq, !atomic_read(&q->queued_count));
         return 0;
 }
 EXPORT_SYMBOL_GPL(vb2_wait_for_all_buffers);
@@ -1689,6 +1729,11 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
 {
         unsigned int i;
 
+        if (q->retry_start_streaming) {
+                q->retry_start_streaming = 0;
+                q->streaming = 0;
+        }
+
         /*
          * Tell driver to stop all transactions and release all queued
          * buffers.
@@ -1738,12 +1783,9 @@ static int vb2_internal_streamon(struct vb2_queue *q, enum v4l2_buf_type type)
         list_for_each_entry(vb, &q->queued_list, queued_entry)
                 __enqueue_in_driver(vb);
 
-        /*
-         * Let driver notice that streaming state has been enabled.
-         */
-        ret = call_qop(q, start_streaming, q, atomic_read(&q->queued_count));
+        /* Tell driver to start streaming. */
+        ret = vb2_start_streaming(q);
         if (ret) {
-                dprintk(1, "streamon: driver refused to start streaming\n");
                 __vb2_queue_cancel(q);
                 return ret;
         }
@@ -2313,15 +2355,15 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
                                 goto err_reqbufs;
                         fileio->bufs[i].queued = 1;
                 }
-
-                /*
-                 * Start streaming.
-                 */
-                ret = vb2_streamon(q, q->type);
-                if (ret)
-                        goto err_reqbufs;
         }
 
+        /*
+         * Start streaming.
+         */
+        ret = vb2_streamon(q, q->type);
+        if (ret)
+                goto err_reqbufs;
+
         q->fileio = fileio;
 
         return ret;
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index ea766525a268..bef53ce555d2 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -252,10 +252,13 @@ struct vb2_buffer {
  *                      receive buffers with @buf_queue callback before
  *                      @start_streaming is called; the driver gets the number
  *                      of already queued buffers in count parameter; driver
- *                      can return an error if hardware fails or not enough
- *                      buffers has been queued, in such case all buffers that
- *                      have been already given by the @buf_queue callback are
- *                      invalidated.
+ *                      can return an error if hardware fails, in that case all
+ *                      buffers that have been already given by the @buf_queue
+ *                      callback are invalidated.
+ *                      If there were not enough queued buffers to start
+ *                      streaming, then this callback returns -ENOBUFS, and the
+ *                      vb2 core will retry calling @start_streaming when a new
+ *                      buffer is queued.
  * @stop_streaming:     called when 'streaming' state must be disabled; driver
  *                      should stop any DMA transactions or wait until they
  *                      finish and give back all buffers it got from buf_queue()
@@ -323,6 +326,9 @@ struct v4l2_fh;
  * @done_wq:    waitqueue for processes waiting for buffers ready to be dequeued
  * @alloc_ctx:  memory type/allocator-specific contexts for each plane
  * @streaming:  current streaming state
+ * @retry_start_streaming: start_streaming() was called, but there were not enough
+ *              buffers queued. If set, then retry calling start_streaming when
+ *              queuing a new buffer.
  * @fileio:     file io emulator internal data, used only if emulator is active
  */
 struct vb2_queue {
@@ -355,6 +361,7 @@ struct vb2_queue {
         unsigned int                    plane_sizes[VIDEO_MAX_PLANES];
 
         unsigned int                    streaming:1;
+        unsigned int                    retry_start_streaming:1;
 
         struct vb2_fileio_data          *fileio;
 };