Re: [PATCH v3 1/3] media: uapi: Introduce new control for video encoder ROI

On 04/08/2026 21:05, Deepa Guthyappa Madivalara wrote:
> Add custom control, V4L2_CID_MPEG_VIDEO_ROI_MB_DELTA_QP for
> video encoder Region of Interest to allow applications to specify
> different quality levels for specific regions in video frames. Define
> V4L2_CID_MPEG_VIDEO_ROI_MB_SIZE to retrieve supported MB size based on
> codec from the hardware encoder and set the corresponding ROI MB delta_qp
> map that adjusts quantization relative to the frame QP's base value.
> 
> This enables use cases like prioritizing quality for faces in video
> conferencing or important objects in surveillance footage while reducing
> bitrate for less critical areas.
> 
> Signed-off-by: Deepa Guthyappa Madivalara <[email protected]>
> ---
>   .../userspace-api/media/v4l/ext-ctrls-codec.rst       | 19 +++++++++++++++++++
>   .../media/v4l/videodev2.h.rst.exceptions              |  1 +
>   .../userspace-api/media/v4l/vidioc-g-ext-ctrls.rst    |  4 ++++
>   .../userspace-api/media/v4l/vidioc-queryctrl.rst      |  6 ++++++
>   include/media/v4l2-ctrls.h                            |  1 +
>   include/uapi/linux/v4l2-controls.h                    |  2 ++
>   include/uapi/linux/videodev2.h                        |  3 +++
>   7 files changed, 36 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index ab865a1a6ba929f1725ce2ab0fd3aeee4a69329a..0f8179de8f742253a5152231592fb8b4355298f7 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -1674,6 +1674,25 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>       Codecs need to always use the specified range, rather then a HW custom range.
>       Applicable to encoders
> 
> +``V4L2_CID_MPEG_VIDEO_ROI_MB_DELTA_QP (__s8)``
> +    This custom control is used to set ROI MB map delta_Qp for whole frame.

"a whole frame" or "the whole frame"

> +    The frame is divided into a grid of MB Size by MB Size pixels (MB Size is
> +    obtained from querying ``V4L2_CID_MPEG_VIDEO_ROI_MB_SIZE``). Each block
> +    is configured with delta_Qp in raster order. The valid range for delta_Qp
> +    is encoder dependent.
> +    Applicable to encoders.
> +
> +``V4L2_CID_MPEG_VIDEO_ROI_MB_SIZE`` (integer)
> +    A read-only control that reports the MB Size used for the ROI delta_QP map.
> +    The supported MB Size depends on the encoder codec.
> +    Only square macroblocks are supported. The value returned represents the

macro-blocks ?

> +    width and height of each block in pixels. The ROI delta_QP map provided
> +    through the ROI control must use the MB Size reported by this control.
> +    The number of entries in the ROI delta_QP array is determined by the
> +    frame dimensions and the reported MB Size. For example, for a QCIF frame
> +    (176x144) if reported MB Size is 16, the delta_QP array must contain
> +    99 entries (176 x 144 / 16 x 16).
> +
>   .. raw:: latex
> 
>       \normalsize
> diff --git a/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions
> index 6182b4e2d2ee002c0d3562e1cc3bc2fd9c4286d6..b036ed3ec2f0744175cad1cbc4e73fe828e0c955 100644
> --- a/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions
> +++ b/Documentation/userspace-api/media/v4l/videodev2.h.rst.exceptions
> @@ -141,6 +141,7 @@ replace symbol V4L2_CTRL_TYPE_STRING :c:type:`V4L.v4l2_ctrl_type`
>   replace symbol V4L2_CTRL_TYPE_U16 :c:type:`V4L.v4l2_ctrl_type`
>   replace symbol V4L2_CTRL_TYPE_U32 :c:type:`V4L.v4l2_ctrl_type`
>   replace symbol V4L2_CTRL_TYPE_U8 :c:type:`V4L.v4l2_ctrl_type`
> +replace symbol V4L2_CTRL_TYPE_S8 :c:type:`V4L.v4l2_ctrl_type`
>   replace symbol V4L2_CTRL_TYPE_MPEG2_SEQUENCE :c:type:`V4L.v4l2_ctrl_type`
>   replace symbol V4L2_CTRL_TYPE_MPEG2_PICTURE :c:type:`V4L.v4l2_ctrl_type`
>   replace symbol V4L2_CTRL_TYPE_MPEG2_QUANTISATION :c:type:`V4L.v4l2_ctrl_type`
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> index d78328152b7552f8f0d30a9e2f7c104bfd4b70d3..fe5f8992389c32d8f35f432229ef2f734002644e 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> @@ -188,6 +188,10 @@ still cause this situation.
>         - ``p_u32``
>         - A pointer to a matrix control of unsigned 32-bit values. Valid if
>   	this control is of type ``V4L2_CTRL_TYPE_U32``.
> +    * - __s8 *
> +      - ``p_s8``
> +      - A pointer to a matrix control of signed 8-bit values. Valid if
> +	this control is of type ``V4L2_CTRL_TYPE_S8``.
>       * - __s32 *
>         - ``p_s32``
>         - A pointer to a matrix control of signed 32-bit values. Valid if
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> index 82c8b52e771ce9301491b3f752e501a8fe7e2434..57e1652ae72e0324742142446acf32a16b94941c 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> @@ -425,6 +425,12 @@ See also the examples in :ref:`control`.
>         - any
>         - An unsigned 32-bit valued control ranging from minimum to maximum
>   	inclusive. The step value indicates the increment between values.
> +    * - ``V4L2_CTRL_TYPE_S8``
> +      - any
> +      - any
> +      - any
> +      - A signed 8-bit valued control ranging from minimum to maximum
> +	inclusive. The step value indicates the increment between values.
>       * - ``V4L2_CTRL_TYPE_MPEG2_QUANTISATION``
>         - n/a
>         - n/a
> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> index 327976b14d50b73a631e4d2ed95d9f4d146c45ab..a1806ddbc797efa52e83cd3f685ef70d5b5483d2 100644
> --- a/include/media/v4l2-ctrls.h
> +++ b/include/media/v4l2-ctrls.h
> @@ -64,6 +64,7 @@ union v4l2_ctrl_ptr {
>   	s32 *p_s32;
>   	s64 *p_s64;
>   	u8 *p_u8;
> +	s8 *p_s8;
>   	u16 *p_u16;
>   	u32 *p_u32;
>   	char *p_char;
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index affec0ab4781507be761cb791ff737460acf9cb7..00a2c48630bd198faa9a2b833a9aa346d8357555 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -920,6 +920,8 @@ enum v4l2_mpeg_video_av1_level {
>   };
> 
>   #define V4L2_CID_MPEG_VIDEO_AVERAGE_QP  (V4L2_CID_CODEC_BASE + 657)
> +#define V4L2_CID_MPEG_VIDEO_ROI_MB_DELTA_QP  (V4L2_CID_CODEC_BASE + 658)
> +#define V4L2_CID_MPEG_VIDEO_ROI_MB_SIZE  (V4L2_CID_CODEC_BASE + 659)
> 
>   /*  MPEG-class control IDs specific to the CX2341x driver as defined by V4L2 */
>   #define V4L2_CID_CODEC_CX2341X_BASE				(V4L2_CTRL_CLASS_CODEC | 0x1000)
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 5373dba640fae3d19247ab1c74ba336e05dc0fe0..3ed343f8c81e0c9240d5a7e5b2dfe365a529fb6c 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1884,6 +1884,7 @@ struct v4l2_ext_control {
>   		__s64 value64;
>   		char __user *string;
>   		__u8 __user *p_u8;
> +		__s8 __user *p_s8;
>   		__u16 __user *p_u16;
>   		__u32 __user *p_u32;
>   		__s32 __user *p_s32;
> @@ -1961,6 +1962,7 @@ enum v4l2_ctrl_type {
>   	V4L2_CTRL_TYPE_U8	     = 0x0100,
>   	V4L2_CTRL_TYPE_U16	     = 0x0101,
>   	V4L2_CTRL_TYPE_U32	     = 0x0102,
> +	V4L2_CTRL_TYPE_S8		 = 0x0103,
>   	V4L2_CTRL_TYPE_AREA          = 0x0106,
>   	V4L2_CTRL_TYPE_RECT	     = 0x0107,
> 
> @@ -1997,6 +1999,7 @@ enum v4l2_ctrl_type {
>   	V4L2_CTRL_TYPE_AV1_TILE_GROUP_ENTRY = 0x281,
>   	V4L2_CTRL_TYPE_AV1_FRAME	    = 0x282,
>   	V4L2_CTRL_TYPE_AV1_FILM_GRAIN	    = 0x283,
> +

stray \n

>   };
> 
>   /*  Used in the VIDIOC_QUERYCTRL ioctl for querying controls */
> 
> --
> 2.34.1
>