Re: [PATCH 2/8] videodev2.h: add V4L2_DEC_CMD_FLUSH

[Alexandre Courbot]

On Fri, Aug 23, 2019 at 4:45 AM Jernej Skrabec <jernej.skrabec@xxxxxxxx> wrote:
>
> From: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
>
> Add this new V4L2_DEC_CMD_FLUSH decoder command and document it.
>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> Signed-off-by: Jernej Skrabec <jernej.skrabec@xxxxxxxx>
> ---
>  Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst | 11 ++++++++++-
>  Documentation/media/videodev2.h.rst.exceptions      |  1 +
>  include/uapi/linux/videodev2.h                      |  1 +
>  3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst b/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst
> index 57f0066f4cff..0bffef6058f7 100644
> --- a/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst
> @@ -208,7 +208,16 @@ introduced in Linux 3.3. They are, however, mandatory for stateful mem2mem decod
>         been started yet, the driver will return an ``EPERM`` error code. When
>         the decoder is already running, this command does nothing. No
>         flags are defined for this command.
> -
> +    * - ``V4L2_DEC_CMD_FLUSH``
> +      - 4
> +      - Flush any held capture buffers. Only valid for stateless decoders,
> +        and only if ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` was set.
> +       This command is typically used when the application reached the
> +       end of the stream and the last output buffer had the
> +       ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag set. This would prevent
> +       dequeueing the last capture buffer containing the last decoded frame.
> +       So this command can be used to explicitly flush that last decoded
> +       frame.

Just for safety, can we also specify that it is valid to call this
command even if no buffer was held (in which case it is a no-op), as
this can help make user-space code simpler?

>
>  Return Value
>  ============
> diff --git a/Documentation/media/videodev2.h.rst.exceptions b/Documentation/media/videodev2.h.rst.exceptions
> index adeb6b7a15cb..a79028e4d929 100644
> --- a/Documentation/media/videodev2.h.rst.exceptions
> +++ b/Documentation/media/videodev2.h.rst.exceptions
> @@ -434,6 +434,7 @@ replace define V4L2_DEC_CMD_START decoder-cmds
>  replace define V4L2_DEC_CMD_STOP decoder-cmds
>  replace define V4L2_DEC_CMD_PAUSE decoder-cmds
>  replace define V4L2_DEC_CMD_RESUME decoder-cmds
> +replace define V4L2_DEC_CMD_FLUSH decoder-cmds
>
>  replace define V4L2_DEC_CMD_START_MUTE_AUDIO decoder-cmds
>  replace define V4L2_DEC_CMD_PAUSE_TO_BLACK decoder-cmds
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 4fa9f543742d..91a79e16089c 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1978,6 +1978,7 @@ struct v4l2_encoder_cmd {
>  #define V4L2_DEC_CMD_STOP        (1)
>  #define V4L2_DEC_CMD_PAUSE       (2)
>  #define V4L2_DEC_CMD_RESUME      (3)
> +#define V4L2_DEC_CMD_FLUSH       (4)
>
>  /* Flags for V4L2_DEC_CMD_START */
>  #define V4L2_DEC_CMD_START_MUTE_AUDIO  (1 << 0)
> --
> 2.22.1
>