Re: [PATCH v6 01/14] videodev2.h: add V4L2_CTRL_FLAG_DYNAMIC_ARRAY

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Hans,

Thank you for the patch.

On Thu, Jun 23, 2022 at 04:31:02PM +0200, Xavier Roumegue wrote:
> From: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> 
> Add a new flag that indicates that this control is a dynamically sized
> array. Also document this flag.
> 
> Currently dynamically sized arrays are limited to one dimensional arrays,
> but that might change in the future if there is a need for it.
> 
> The initial use-case of dynamic arrays are stateless codecs. A frame
> can be divided in many slices, so you want to provide an array containing
> slice information for each slice. Typically the number of slices is small,
> but the standard allow for hundreds or thousands of slices. Dynamic arrays
> are a good solution since sizing the array for the worst case would waste
> substantial amounts of memory.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

> ---
>  .../userspace-api/media/v4l/vidioc-queryctrl.rst          | 8 ++++++++
>  include/uapi/linux/videodev2.h                            | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> index 88f630252d98..a20dfa2a933b 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> @@ -625,6 +625,14 @@ See also the examples in :ref:`control`.
>  	``V4L2_CTRL_FLAG_GRABBED`` flag when buffers are allocated or
>  	streaming is in progress since most drivers do not support changing
>  	the format in that case.
> +    * - ``V4L2_CTRL_FLAG_DYNAMIC_ARRAY``
> +      - 0x0800
> +      - This control is a dynamically sized 1-dimensional array. It
> +        behaves the same as a regular array, except that the number
> +	of elements as reported by the ``elems`` field is between 1 and
> +	``dims[0]``. So setting the control with a differently sized
> +	array will change the ``elems`` field when the control is
> +	queried afterwards.
>  
>  Return Value
>  ============
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 343b95107fce..5c45ca18fac9 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1889,6 +1889,7 @@ struct v4l2_querymenu {
>  #define V4L2_CTRL_FLAG_HAS_PAYLOAD	0x0100
>  #define V4L2_CTRL_FLAG_EXECUTE_ON_WRITE	0x0200
>  #define V4L2_CTRL_FLAG_MODIFY_LAYOUT	0x0400
> +#define V4L2_CTRL_FLAG_DYNAMIC_ARRAY	0x0800
>  
>  /*  Query flags, to be ORed with the control ID */
>  #define V4L2_CTRL_FLAG_NEXT_CTRL	0x80000000

-- 
Regards,

Laurent Pinchart