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b=ZJzfy1N3ynUaMcXRgYRv1SaGEp9n3diop+9Bju3fdiCxK34zVFboSYxl3XHmPqQUv mTEbLSRI/UujaX3ZLtazI6zh7SW9UX8Vaqey+EcSs3xhFRNo5a0I6R7tCC5ivnC/HX HSRZRJHH5Ttqd9k0YR5xaEpV7xI2z5cOJqnxqDjU= Message-ID: <9b12b035-a80d-4d12-a039-daa94d13280e@ideasonboard.com> Date: Wed, 9 Jul 2025 12:33:17 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/8] media: uapi: Introduce V4L2 extensible params To: Jacopo Mondi , Dafna Hirschfeld , Laurent Pinchart , Keke Li , Mauro Carvalho Chehab , Heiko Stuebner , Sakari Ailus Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org References: <20250708-extensible-parameters-validation-v1-0-9fc27c9c728c@ideasonboard.com> <20250708-extensible-parameters-validation-v1-1-9fc27c9c728c@ideasonboard.com> Content-Language: en-US From: Dan Scally Autocrypt: addr=dan.scally@ideasonboard.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Jacopo - thanks for the patches On 08/07/2025 11:40, 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 > parameters format. > > 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 newly introduced header is not meant to be used directly by > applications which should instead use the platform-specific ones. > > Signed-off-by: Jacopo Mondi > --- > MAINTAINERS | 6 ++ > include/uapi/linux/media/v4l2-extensible-params.h | 106 ++++++++++++++++++++++ > 2 files changed, 112 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 > +L: linux-media@vger.kernel.org > +S: Maintained > +F: include/uapi/linux/media/v4l2-extensible-params.h > + > VF610 NAND DRIVER > M: Stefan Agner > L: linux-mtd@lists.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..ed37da433c6b1a34523b6a9befde5c0dee601cfb > --- /dev/null > +++ b/include/uapi/linux/media/v4l2-extensible-params.h > @@ -0,0 +1,106 @@ > +/* 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 > + */ > + > +#ifndef _UAPI_V4L2_PARAMS_H_ > +#define _UAPI_V4L2_PARAMS_H_ > + > +#ifndef _UAPI_V4L2_EXTENSIBLE_PARAMS_GUARD_ > +/* > + * Note: each ISP driver exposes a different uAPI, where the types layout > + * match (more or less strictly) the hardware registers layout. > + * > + * This file defines the base types on which each ISP driver can implement its > + * own types that define its uAPI. > + * > + * This file is not meant to be included directly by applications which shall > + * instead only include the ISP-specific implementation. > + */ > +#error "This file should not be included directly by applications" > +#endif > + > +#include > + > +/** > + * struct v4l2_params_block - V4L2 extensible parameters block header struct v4l2_params_block_header would be nicer I think > + * > + * 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 platform-specific control flags. Since we're including flags in this base struct rather than a platform specific subclass I think perhaps we should centralise some flags (which I think is supported by the fact that all three implementations share the same flags so far). Perhaps we could reserve the bottom 8 bits for common flags (like ENABLE / DISABLE) and validate them centrally, and leave the top 8 for platform specific flags. I think we could then drop the platform specific validation for rkisp1 and c3 and just pass null to the helpers, since they do the same thing. > + * > + * Userspace shall never use this type directly but use the platform specific > + * one with the associated data types. Why wouldn't userspace just use these directly? I could see why it might be difficult for the C3 and Rkisp1 which are merged, but for a new implementation couldn't they just use these objects without bothering to define their own? If we end up using these objects directly I think it would be nice to have the example code block from the platform specific headers documentation here too. > + * > + * - Rockchip RkISP1: :c:type:`rkisp1_ext_params_block_type` > + * - Amlogic C3: :c:type:`c3_isp_params_block_type` > + * > + * @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 { > + __u16 type; > + __u16 flags; > + __u32 size; > +} __attribute__((aligned(8))); > + > +/** > + * 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` 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. > + * > + * Each ISP driver using the extensible parameters format shall define a > + * type which is type-convertible to this one, with the difference that the > + * @data member shall actually a memory buffer of platform-specific size and > + * not a pointer. Why not just use this object directly? We could provide a helper in v4l2-extensible-params.h that calculates the size of the buffer with a given data array size for the driver's convenience Thanks Dan > + * > + * Userspace shall never use this type directly but use the platform specific > + * one with the associated data types. > + * > + * - 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_ */ >