Message-ID: <8fee18e6-9955-4b51-8b6b-e70029ec47eb@ideasonboard.com>
Date: Thu, 10 Jul 2025 15:49:30 +0100
From: Dan Scally <dan.scally@...asonboard.com>
To: Jacopo Mondi <jacopo.mondi@...asonboard.com>,
 Dafna Hirschfeld <dafna@...tmail.com>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Keke Li <keke.li@...ogic.com>, Mauro Carvalho Chehab <mchehab@...nel.org>,
 Heiko Stuebner <heiko@...ech.de>, Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/8] media: uapi: Introduce V4L2 extensible params

Hi Jacopo

On 10/07/2025 14:52, Jacopo Mondi wrote:
> Introduce v4l2-extensible-params.h in the Linux kernel uAPI.
>
> The header defines two types that all drivers that use the extensible
> parameters format for ISP configuration shall use to build their own
> format versions.
>
> The newly introduce type v4l2_params_block represent the
> header to be prepend to each ISP configuration block and the
> v4l2_params_buffer type represent the base type for the configuration
> parameters buffer.
>
> The v4l2_params_buffer represents the container for the ISP
> configuration data block. The generic type is defined with a 0-sized
> data block that specific ISP implementation shall properly size
> according to their capabilities.
>
> [Add v4l2_params_buffer_size()]
> Signed-off-by: Daniel Scally <dan.scally@...asonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo.mondi@...asonboard.com>
> ---
>   MAINTAINERS                                       |   6 +
>   include/uapi/linux/media/v4l2-extensible-params.h | 144 ++++++++++++++++++++++
>   2 files changed, 150 insertions(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 658543062bba3b7e600699d7271ffc89250ba7e5..49a9329e5fe8874bdbaca13946ea28bd80134cb3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -25968,6 +25968,12 @@ F:	drivers/media/i2c/vd55g1.c
>   F:	drivers/media/i2c/vd56g3.c
>   F:	drivers/media/i2c/vgxy61.c
>   
> +V4L2 EXTENSIBLE PARAMETERS FORMAT
> +M:	Jacopo Mondi <jacopo.mondi@...asonboard.com>
> +L:	linux-media@...r.kernel.org
> +S:	Maintained
> +F:	include/uapi/linux/media/v4l2-extensible-params.h
> +
>   VF610 NAND DRIVER
>   M:	Stefan Agner <stefan@...er.ch>
>   L:	linux-mtd@...ts.infradead.org
> diff --git a/include/uapi/linux/media/v4l2-extensible-params.h b/include/uapi/linux/media/v4l2-extensible-params.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..ace89299a4b37e428c0bc9a72fbc079b1dcda91a
> --- /dev/null
> +++ b/include/uapi/linux/media/v4l2-extensible-params.h
> @@ -0,0 +1,144 @@
> +/* SPDX-License-Identifier: ((GPL-2.0+ WITH Linux-syscall-note) OR MIT) */
> +/*
> + * Video4Linux2 extensible configuration parameters base types
> + *
> + * Copyright (C) 2025 Ideas On Board Oy
> + * Author: Jacopo Mondi <jacopo.mondi@...asonboard.com>
> + */
> +
> +#ifndef _UAPI_V4L2_PARAMS_H_
> +#define _UAPI_V4L2_PARAMS_H_
> +
> +#include <linux/types.h>
> +
> +#define V4L2_PARAMS_FL_BLOCK_DISABLE	(1U << 0)
> +#define V4L2_PARAMS_FL_BLOCK_ENABLE	(1U << 1)


Actually I wonder if a "V4L2_PARAMS_BLOCK_FL_NONE    0" is worthwhile to clear them explicitly?

> +
> +/*
> + * Reserve the first 8 bits for V4L2_PARAMS_FL_* flag. Platform-specific flags
> + * should be defined as:
> + * #define PLATFORM_SPECIFIC_FLAG0	((1U << V4L2_PARAMS_FL_PLATFORM_FLAGS(0))
> + * #define PLATFORM_SPECIFIC_FLAG1	((1U << V4L2_PARAMS_FL_PLATFORM_FLAGS(1))
> + */
> +#define V4L2_PARAMS_FL_PLATFORM_FLAGS(n)	((n) << 8)
> +
> +/**
> + * struct v4l2_params_block_header - V4L2 extensible parameters block header
> + *
> + * This structure represents the common part of all the ISP configuration
> + * blocks. Each parameters block shall embed an instance of this structure type
> + * as its first member, followed by the block-specific configuration data. The
> + * driver inspects this common header to discern the block type and its size and
> + * properly handle the block content by casting it to the correct block-specific
> + * type.
> + *
> + * The @type field is one of the values enumerated by each platform-specific ISP
> + * block types which specifies how the data should be interpreted by the driver.
> + * The @size field specifies the size of the parameters block and is used by the
> + * driver for validation purposes.
> + *
> + * The @flags field is a bitmask of per-block flags V4L2_PARAMS_FL_* and
> + * platform-specific flags specified by the platform-specific header.
> + *
> + * Documentation of the platform-specific flags handling is specified by the
> + * platform-specific block header type:
> + *
> + * - Rockchip RkISP1: :c:type:`rkisp1_ext_params_block_type`
> + * - Amlogic C3: :c:type:`c3_isp_params_block_type`
> + *
> + * Userspace is responsible for correctly populating the parameters block header
> + * fields (@type, @flags and @size) and the block-specific parameters.
> + *
> + * @type: The parameters block type (platform-specific)
> + * @flags: A bitmask of block flags (platform-specific)
> + * @size: Size (in bytes) of the parameters block, including this header
> + */
> +struct v4l2_params_block_header {
> +	__u16 type;
> +	__u16 flags;
> +	__u32 size;
> +} __attribute__((aligned(8)));
> +
> +/**
> + * v4l2_params_buffer_size - Calculate size of v4l2_params_buffer for a platform
> + *
> + * Users of the v4l2 extensible parameters will have differing sized data arrays
> + * depending on their specific parameter buffers. Drivers and userspace will
> + * need to be able to calculate the appropriate size of the struct to
> + * accommodate all ISP configuration blocks provided by the platform.
> + * This macro provides a convenient tool for the calculation.
> + *
> + * Each driver shall provide a definition of their extensible parameters
> + * implementation data buffer size. As an example:
> + *
> + * #define PLATFORM_BLOCKS_MAX_SIZE		\
> + *	sizeof(platform_block_0)	+	\
> + *	sizeof(platform_block_1)
> + *
> + * #define PLATFORM_BUFFER_SIZE			\
> + *	v4l2_params_buffer_size(PLATFORM_BLOCKS_MAX_SIZE)
> + *
> + * Drivers are then responsible for allocating buffers of the proper size
> + * by assigning PLATFORM_BUFFER_SIZE to the per-plane size of the videobuf2
> + * .queue_setup() operation and userspace shall use PLATFORM_BUFFER_SIZE
> + * when populating the ISP configuration data buffer.
> + *
> + * @max_params_size: The total size of the ISP configuration blocks
> + */
> +#define v4l2_params_buffer_size(max_params_size) \
> +	(offsetof(struct v4l2_params_buffer, data) + (max_params_size))
> +
> +/**
> + * struct v4l2_params_buffer - V4L2 extensible parameters configuration
> + *
> + * This struct contains the configuration parameters of the ISP algorithms,
> + * serialized by userspace into a data buffer. Each configuration parameter
> + * block is represented by a block-specific structure which contains a
> + * :c:type:`v4l2_params_block_header` entry as first member. Userspace populates
> + * the @data buffer with configuration parameters for the blocks that it intends
> + * to configure. As a consequence, the data buffer effective size changes
> + * according to the number of ISP blocks that userspace intends to configure and
> + * is set by userspace in the @data_size field.
> + *
> + * The parameters buffer is versioned by the @version field to allow modifying
> + * and extending its definition. Userspace shall populate the @version field to
> + * inform the driver about the version it intends to use. The driver will parse
> + * and handle the @data buffer according to the data layout specific to the
> + * indicated version and return an error if the desired version is not
> + * supported.
> + *
> + * For each ISP block that userspace wants to configure, a block-specific
> + * structure is appended to the @data buffer, one after the other without gaps
> + * in between nor overlaps. Userspace shall populate the @data_size field with
> + * the effective size, in bytes, of the @data buffer.
> + *
> + * Drivers shall take care of properly sizing of the extensible parameters
> + * buffer @data array. The v4l2_params_buffer type is defined with a
> + * flexible-array-member at the end, which resolves to a size of 0 bytes when
> + * inspected with sizeof(struct v4l2_params_buffer). This of course is not
> + * suitable for neither buffer allocation in the kernel driver nor for proper
> + * handling in userspace of the @data buffer it has to populate.
> + *
> + * Drivers using this type in their userspace API definition are responsible
> + * for providing the exact definition of the @data buffer size using the
> + * v4l2_params_buffer_size() macro. The size shall be used
> + * by the driver for buffers allocation and by userspace for populating the
> + * @data buffer before queueing it to the driver
> + *
> + * Drivers that were already using extensible-parameters before the introduction
> + * of this file define their own type-convertible implementation of this
> + * type, see:
> + * - Rockchip RkISP1: :c:type:`rkisp1_ext_params_cfg`
> + * - Amlogic C3: :c:type:`c3_isp_params_cfg`
> + *
> + * @version: The parameters buffer version (platform-specific)
> + * @data_size: The configuration data effective size, excluding this header
> + * @data: The configuration data
> + */
> +struct v4l2_params_buffer {
> +	__u32 version;
> +	__u32 data_size;
> +	__u8 data[];
> +};
> +
> +#endif /* _UAPI_V4L2_PARAMS_H_ */
>

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