Re: [PATCH 2/8] uapi: videodev2: Add V4L2_META_FMT_RK_ISP1_EXT_PARAMS

[Dan Scally <dan.scally@ideasonboard.com>]

Hi Jacopo

On 05/06/2024 17:54, Jacopo Mondi wrote:
> Add a new format definition for the RkISP1 extensible parameters
> format and document it.
>
> Document the usage of the new format in the rkisp1 admin guide.
>
> Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
> ---
>   Documentation/admin-guide/media/rkisp1.rst    | 11 +++-
>   .../media/v4l/metafmt-rkisp1.rst              | 62 ++++++++++++++++---
>   drivers/media/v4l2-core/v4l2-ioctl.c          |  1 +
>   include/uapi/linux/videodev2.h                |  1 +
>   4 files changed, 64 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/admin-guide/media/rkisp1.rst b/Documentation/admin-guide/media/rkisp1.rst
> index 6f14d9561fa5..934c25e191df 100644
> --- a/Documentation/admin-guide/media/rkisp1.rst
> +++ b/Documentation/admin-guide/media/rkisp1.rst
> @@ -114,11 +114,18 @@ to be applied to the hardware during a video stream, allowing userspace
>   to dynamically modify values such as black level, cross talk corrections
>   and others.
>   
> -The buffer format is defined by struct :c:type:`rkisp1_params_cfg`, and
> -userspace should set
> +The ISP driver supports two different parameters configuration methods, the
> +`fixed parameters format` or the `extensible parameters format`.
> +
> +When using the `fixed parameters` method the buffer format is defined by struct
> +:c:type:`rkisp1_params_cfg`, and userspace set
>   :ref:`V4L2_META_FMT_RK_ISP1_PARAMS <v4l2-meta-fmt-rk-isp1-params>` as the
>   dataformat.
>   
> +When using the fixed parameters method the buffer format is defined by struct
> +:c:type:`rkisp1_ext_params_cfg`, and userspace set
s/set/should set
> +:ref:`V4L2_META_FMT_RK_ISP1_EXT_PARAMS <v4l2-meta-fmt-rk-isp1-ext-params>` as
> +the dataformat.
>   
>   Capturing Video Frames Example
>   ==============================
> diff --git a/Documentation/userspace-api/media/v4l/metafmt-rkisp1.rst b/Documentation/userspace-api/media/v4l/metafmt-rkisp1.rst
> index fa04f00bcd2e..6ff776d071a3 100644
> --- a/Documentation/userspace-api/media/v4l/metafmt-rkisp1.rst
> +++ b/Documentation/userspace-api/media/v4l/metafmt-rkisp1.rst
> @@ -1,28 +1,72 @@
>   .. SPDX-License-Identifier: GPL-2.0
>   
> -.. _v4l2-meta-fmt-rk-isp1-params:
> -
>   .. _v4l2-meta-fmt-rk-isp1-stat-3a:
>   
> -*****************************************************************************
> -V4L2_META_FMT_RK_ISP1_PARAMS ('rk1p'), V4L2_META_FMT_RK_ISP1_STAT_3A ('rk1s')
> -*****************************************************************************
> +************************************************************************************************************************
> +V4L2_META_FMT_RK_ISP1_PARAMS ('rk1p'), V4L2_META_FMT_RK_ISP1_STAT_3A ('rk1s'), V4L2_META_FMT_RK_ISP1_EXT_PARAMS ('rk1e')
> +************************************************************************************************************************
>   
> +========================
>   Configuration parameters
>   ========================
>   
> -The configuration parameters are passed to the
> +The configuration of the RkISP1 ISP is performed by userspace by providing
> +parameters for the ISP to the driver using the :c:type:`v4l2_meta_format`
> +interface.
> +
> +There are currently two methods that allow to configure the ISP, the `fixed
> +parameters` configuration format and the `extensible parameters` configuration
> +format.
> +
> +.. _v4l2-meta-fmt-rk-isp1-params:
> +
> +Fixed parameters configuration format
> +=====================================
> +
> +When using the fixed configuration format, parameters are passed to the
>   :ref:`rkisp1_params <rkisp1_params>` metadata output video node, using
> -the :c:type:`v4l2_meta_format` interface. The buffer contains
> -a single instance of the C structure :c:type:`rkisp1_params_cfg` defined in
> -``rkisp1-config.h``. So the structure can be obtained from the buffer by:
> +the `V4L2_META_FMT_RK_ISP1_PARAMS` meta pixel format.
> +
> +The buffer contains a single instance of the C structure
> +:c:type:`rkisp1_params_cfg` defined in ``rkisp1-config.h``. So the structure can
> +be obtained from the buffer by:
>   
>   .. code-block:: c
>   
>   	struct rkisp1_params_cfg *params = (struct rkisp1_params_cfg*) buffer;
>   
> +As the members of :c:type:`rkisp1_params_cfg` are defined in the
> +``rkisp1-config.h`` header, the structure layout is immutable and cannot be
> +extended further. For this reason the fixed configuration format only allows the
> +configuration of the ISP blocks supported at the time when the structure had
> +been defined in the header file, as introducing new parameters or modifying the
> +existing ones would change the buffer layout and cause breakages in existing
> +applications.


I'm not sure I'd bother with the last sentence; up to you though. Possibly a quick explainer as to 
why there's two separate methods and why the extensible one should be preferred could be in the 
"Configuration parameters" section instead.

> +
> +.. _v4l2-meta-fmt-rk-isp1-ext-params:
> +
> +Extensible parameters configuration format
> +==========================================
> +
> +When using the extensible configuration format, parameters are passed to the
> +:ref:`rkisp1_params <rkisp1_params>` metadata output video node, using
> +the `V4L2_META_FMT_RK_ISP1_EXT_PARAMS` meta pixel format.
> +
> +The buffer contains a single instance of the C structure
> +:c:type:`rkisp1_ext_params_cfg` defined in ``rkisp1-config.h``. The
> +:c:type:`rkisp1_ext_params_cfg` structure is designed to allow userspace to
> +populate the data buffer with only the configuration data for the ISP block it
s/block/block(s)?
> +intends to configure. The extensible parameters format design allows to define
> +new block types and new configuration parameters and defines a versioning scheme
Perhaps "allows developers to define new block types to support new configuration parameters"?
> +so that it can be extended and versioned without breaking compatibility with
> +existing applications.
> +
> +For these reasons, this configuration method if preferred over the `fixed
> +parameters` format alternative.
> +
>   .. rkisp1_stat_buffer
>   
> +===========================
>   3A and histogram statistics
>   ===========================
>   
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 4c76d17b4629..aefdc1efd24b 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1456,6 +1456,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>   	case V4L2_META_FMT_VIVID:       descr = "Vivid Metadata"; break;
>   	case V4L2_META_FMT_RK_ISP1_PARAMS:	descr = "Rockchip ISP1 3A Parameters"; break;
>   	case V4L2_META_FMT_RK_ISP1_STAT_3A:	descr = "Rockchip ISP1 3A Statistics"; break;
> +	case V4L2_META_FMT_RK_ISP1_EXT_PARAMS:	descr = "Rockchip ISP1 Ext 3A Params"; break;

I think spell out "Extensible" personally; we already allow breaking like length limits here.


Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>

>   	case V4L2_PIX_FMT_NV12_8L128:	descr = "NV12 (8x128 Linear)"; break;
>   	case V4L2_PIX_FMT_NV12M_8L128:	descr = "NV12M (8x128 Linear)"; break;
>   	case V4L2_PIX_FMT_NV12_10BE_8L128:	descr = "10-bit NV12 (8x128 Linear, BE)"; break;
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index fe6b67e83751..7c2a303c6f59 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -840,6 +840,7 @@ struct v4l2_pix_format {
>   /* Vendor specific - used for RK_ISP1 camera sub-system */
>   #define V4L2_META_FMT_RK_ISP1_PARAMS	v4l2_fourcc('R', 'K', '1', 'P') /* Rockchip ISP1 3A Parameters */
>   #define V4L2_META_FMT_RK_ISP1_STAT_3A	v4l2_fourcc('R', 'K', '1', 'S') /* Rockchip ISP1 3A Statistics */
> +#define V4L2_META_FMT_RK_ISP1_EXT_PARAMS	v4l2_fourcc('R', 'K', '1', 'E') /* Rockchip ISP1 3a Extensible Parameters */
>   
>   #ifdef __KERNEL__
>   /*