Hi Hans
On Mon, 9 Dec 2013, Hans Verkuil wrote:
> From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>
> If start_streaming returns -ENODATA, then it will be retried the next time
> a buffer is queued.
Wouldn't ENOBUFS be a better error code?
Thanks
Guennadi
> This means applications no longer need to know how many
> buffers need to be queued before STREAMON can be called. This is particularly
> useful for output stream I/O.
>
> If a DMA engine needs at least X buffers before it can start streaming, then
> for applications to get a buffer out as soon as possible they need to know
> the minimum number of buffers to queue before STREAMON can be called. You can't
> just try STREAMON after every buffer since on failure STREAMON will dequeue
> all your buffers. (Is that a bug or a feature? Frankly, I'm not sure).
>
> This patch simplifies applications substantially: they can just call STREAMON
> at the beginning and then start queuing buffers and the DMA engine will
> kick in automagically once enough buffers are available.
>
> This also fixes using write() to stream video: the fileio implementation
> calls streamon without having any queued buffers, which will fail today for
> any driver that requires a minimum number of buffers.
>
> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> Acked-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> drivers/media/v4l2-core/videobuf2-core.c | 68 ++++++++++++++++++++++++++------
> include/media/videobuf2-core.h | 15 +++++--
> 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 f0b3683..00a3f98 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1356,6 +1356,39 @@ 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 -ENODATA and you have to
> + * retry when the next buffer is queued.
> + */
> + if (ret == -ENODATA) {
> + 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");
> @@ -1404,6 +1437,12 @@ 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;
> }
> @@ -1553,7 +1592,8 @@ 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);
> @@ -1667,6 +1707,11 @@ 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.
> @@ -1716,12 +1761,9 @@ 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;
> }
> @@ -2291,15 +2333,15 @@ 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 67972f6..d2a823e 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 -ENODATA, 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;
> };
> --
> 1.8.4.3
>
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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