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

[Alexandre Courbot]

On Fri, Aug 30, 2019 at 6:45 PM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote:
>
> On 8/30/19 11:38 AM, Alexandre Courbot wrote:
> > 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?
>
> Ah yes, thanks for the reminder.
>
> Jernej, when you post the next version of this series, can you change the text
> above to:
>
> - Flush any held capture buffers. Only valid for stateless decoders.
>   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 capture buffer containing the last decoded frame.
>   So this command can be used to explicitly flush that final decoded
>   frame. This command does nothing if there are no held capture buffers.

With the above,

Reviewed-by: Alexandre Courbot <acourbot@xxxxxxxxxxxx>

Thanks!

>
> Regards,
>
>         Hans
>
> >
> >>
> >>  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
> >>
>