linux-kernel - Re: [RFC v4 05/17] [media] v4l: add V4L2_EVENT_OUT

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Date:   Tue, 24 Oct 2017 15:09:06 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Gustavo Padovan <gustavo@...ovan.org>, linux-media@...r.kernel.org
Cc:     Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [RFC v4 05/17] [media] v4l: add V4L2_EVENT_OUT_FENCE event

On 10/20/2017 11:50 PM, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.com>
> 
> Add a new event the userspace can subscribe to receive notifications
> of the out_fence_fd when a buffer is queued onto the driver.
> The event provides the index of the queued buffer and the out_fence_fd.
> 
> v3: - Rename event to V4L2_EVENT_OUT_FENCE
> 
> v2: - Add missing Documentation (Mauro)
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
> ---
>  Documentation/media/uapi/v4l/vidioc-dqevent.rst | 23 +++++++++++++++++++++++
>  Documentation/media/videodev2.h.rst.exceptions  |  1 +
>  include/uapi/linux/videodev2.h                  | 12 ++++++++++++
>  3 files changed, 36 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/vidioc-dqevent.rst b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> index cb3565f36793..2143df63aeb1 100644
> --- a/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> @@ -79,6 +79,10 @@ call.
>        - ``src_change``
>        - Event data for event V4L2_EVENT_SOURCE_CHANGE.
>      * -
> +      - struct :c:type:`v4l2_event_buf_queued`
> +      - ``buf_queued``
> +      - Event data for event V4L2_EVENT_OUT_FENCE.
> +    * -
>        - __u8
>        - ``data``\ [64]
>        - Event data. Defined by the event type. The union should be used to
> @@ -338,6 +342,25 @@ call.
>  	each cell in the motion detection grid, then that all cells are
>  	automatically assigned to the default region 0.
>  
> +.. c:type:: v4l2_event_out_fence
> +
> +.. flat-table:: struct v4l2_event_out_fence
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths:       1 1 2
> +
> +    * - __u32
> +      - ``index``
> +      - The index of the buffer that was queued to the driver.
> +    * - __s32
> +      - ``out_fence_fd``
> +      - The out-fence file descriptor of the buffer that was queued to
> +	the driver. It will signal when the buffer is ready, or if an
> +	error happens.

What happens when the buffer has already been dequeued? This needs to be defined.

Perhaps set out_fence_fd to 0 or -1 in that case?

Regards,

	Hans

> +
> +
> +
> +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
>  
>  
>  .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
> diff --git a/Documentation/media/videodev2.h.rst.exceptions b/Documentation/media/videodev2.h.rst.exceptions
> index a5cb0a8686ac..32f3d5b37e3a 100644
> --- a/Documentation/media/videodev2.h.rst.exceptions
> +++ b/Documentation/media/videodev2.h.rst.exceptions
> @@ -462,6 +462,7 @@ replace define V4L2_EVENT_CTRL event-type
>  replace define V4L2_EVENT_FRAME_SYNC event-type
>  replace define V4L2_EVENT_SOURCE_CHANGE event-type
>  replace define V4L2_EVENT_MOTION_DET event-type
> +replace define V4L2_EVENT_OUT_FENCE event-type
>  replace define V4L2_EVENT_PRIVATE_START event-type
>  
>  replace define V4L2_EVENT_CTRL_CH_VALUE ctrl-changes-flags
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 185d6a0acc06..2a432e8c18e3 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2156,6 +2156,7 @@ struct v4l2_streamparm {
>  #define V4L2_EVENT_FRAME_SYNC			4
>  #define V4L2_EVENT_SOURCE_CHANGE		5
>  #define V4L2_EVENT_MOTION_DET			6
> +#define V4L2_EVENT_OUT_FENCE			7
>  #define V4L2_EVENT_PRIVATE_START		0x08000000
>  
>  /* Payload for V4L2_EVENT_VSYNC */
> @@ -2208,6 +2209,16 @@ struct v4l2_event_motion_det {
>  	__u32 region_mask;
>  };
>  
> +/**
> + * struct v4l2_event_out_fence - out fence fd event
> + * @index:		index of the buffer queued in the driver
> + * @out_fence_fd:	out-fence fd of the buffer queued
> + */
> +struct v4l2_event_out_fence {
> +	__u32 index;
> +	__s32 out_fence_fd;
> +};
> +
>  struct v4l2_event {
>  	__u32				type;
>  	union {
> @@ -2216,6 +2227,7 @@ struct v4l2_event {
>  		struct v4l2_event_frame_sync	frame_sync;
>  		struct v4l2_event_src_change	src_change;
>  		struct v4l2_event_motion_det	motion_det;
> +		struct v4l2_event_out_fence	out_fence;
>  		__u8				data[64];
>  	} u;
>  	__u32				pending;
>