[1/4] include: linux: Add v4l2-extensible-params.h

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diff --git a/include/linux/media/v4l2-extensible-params.h b/include/linux/media/v4l2-extensible-params.h
new file mode 100644
index 0000000000000000000000000000000000000000..2b93b5b4c04b3d29ddb7d509b4cbde64238d8c20
--- /dev/null
+++ b/include/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@ideasonboard.com>
+ */
+
+#ifndef _V4L2_PARAMS_H_
+#define _V4L2_PARAMS_H_
+
+#include <linux/types.h>
+
+#define V4L2_PARAMS_FL_BLOCK_DISABLE	(1U << 0)
+#define V4L2_PARAMS_FL_BLOCK_ENABLE	(1U << 1)
+
+/*
+ * 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 /* _V4L2_PARAMS_H_ */