Re: [PATCH v5 1/8] media: uapi: Introduce V4L2 generic ISP types

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, Oct 06, 2025 at 09:15:47AM +0100, Daniel Scally wrote:
> On 05/10/2025 01:06, Laurent Pinchart wrote:
> > On Mon, Sep 15, 2025 at 07:18:10PM +0200, Jacopo Mondi wrote:
> >> Introduce v4l2-isp.h in the Linux kernel uAPI.
> >>
> >> The header includes types for generic ISP configuration parameters
> >> and will be extended in future with support for generic ISP statistics
> > 
> > s/in future/in the future/
> > 
> > (and you can reflow the commit message)
> > 
> >> formats.
> >>
> >> Generic ISP parameters support is provided by introducing two new
> >> types that represent an extensible and versioned buffer of ISP
> >> configuration parameters.
> >>
> >> The v4l2_params_block_header structure represents the header to be
> >> prepend to each ISP configuration block and the v4l2_params_buffer type
> >> represents the base type for the configuration parameters buffer.
> > 
> > The second part of the sentence describes the same structure as the next
> > paragraph.
> > 
> >> The v4l2_params_buffer represents the container for the ISP
> >> configuration data block. The generic type is defined with a 0-sized
> >> data member that the ISP driver implementations shall properly size
> >> according to their capabilities.
> > 
> > This will be easier to understand if you describe v4l2_params_buffer
> > first.
> > 
> > The commit message would benefit from being rewritten.
> > 
> >> [Add v4l2_params_buffer_size()]
> >> Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
> >> Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
> >> Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
> >> ---
> >>   MAINTAINERS                         |   6 +++
> >>   include/uapi/linux/media/v4l2-isp.h | 100 ++++++++++++++++++++++++++++++++++++
> >>   2 files changed, 106 insertions(+)
> >>
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index ee8cb2db483f6a5e96b62b6f2edd05b1427b69f5..e82c3d0758d6033fe8fcd56ffde2c03c4319fd11 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -26410,6 +26410,12 @@ F:	drivers/media/i2c/vd55g1.c
> >>   F:	drivers/media/i2c/vd56g3.c
> >>   F:	drivers/media/i2c/vgxy61.c
> >>   
> >> +V4L2 GENERIC ISP PARAMETERS AND STATISTIC FORMATS
> >> +M:	Jacopo Mondi <jacopo.mondi@ideasonboard.com>
> >> +L:	linux-media@vger.kernel.org
> >> +S:	Maintained
> >> +F:	include/uapi/linux/media/v4l2-isp.h
> >> +
> >>   VF610 NAND DRIVER
> >>   M:	Stefan Agner <stefan@agner.ch>
> >>   L:	linux-mtd@lists.infradead.org
> >> diff --git a/include/uapi/linux/media/v4l2-isp.h b/include/uapi/linux/media/v4l2-isp.h
> >> new file mode 100644
> >> index 0000000000000000000000000000000000000000..b838555dce2b290a14136ab09ea4d2dfdc95b26b
> >> --- /dev/null
> >> +++ b/include/uapi/linux/media/v4l2-isp.h
> >> @@ -0,0 +1,100 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> >> +/*
> >> + * Video4Linux2 generic ISP parameters and statistics support
> >> + *
> >> + * Copyright (C) 2025 Ideas On Board Oy
> >> + * Author: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
> >> + */
> >> +
> >> +#ifndef _UAPI_V4L2_ISP_H_
> >> +#define _UAPI_V4L2_ISP_H_
> >> +
> >> +#include <linux/stddef.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.
> >> + *
> >> + * Driver-specific flags should be defined as:
> >> + * #define PLATFORM_SPECIFIC_FLAG0     ((1U << V4L2_PARAMS_FL_DRIVER_FLAGS(0))
> > 
> > s/PLATFORM/DRIVER/
> > 
> >> + * #define PLATFORM_SPECIFIC_FLAG1     ((1U << V4L2_PARAMS_FL_DRIVER_FLAGS(1))
> >> + */
> >> +#define V4L2_PARAMS_FL_DRIVER_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.
> > 
> > The last sentence is not relevant for the UAPI.
> > 
> >> + *
> >> + * The @type field is an ISP driver-specific value that identifies the block
> >> + * type. The @size field specifies the size of the parameters block.
> >> + *
> >> + * The @flags field is a bitmask of per-block flags V4L2_PARAMS_FL_* and
> >> + * driver-specific flags specified by the driver header.
> >> + *
> >> + * @type: The parameters block type (driver-specific)
> >> + * @flags: A bitmask of block flags (driver-specific)
> >> + * @size: Size (in bytes) of the parameters block, including this header
> > 
> > I think the fields usually go right after the structure name, followed
> > by the rest of the documentation.
> > 
> >> + */
> >> +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.
> >> + *
> >> + * @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))
> > 
> > This isn't used in this series as far as I can tell, and neither is it
> > used in your libcamera implementation. I'd drop the macro (as well as
> > the mention in the commit message).
> 
> This is because the rkisp1 and c3 ISP implementations are already merged with a custom parameters 
> buffer struct defined at [1] and [2]. There the array size is set to the max size macro. This series 
> just asserts that the header part is a size match for struct v4l2_params_buffer to guarantee 
> compatibility, so throughout those drivers they can use sizeof(struct c3_isp_params_cfg) or the 
> rkisp equivalent and it's fine.
> 
> For new users that don't have a custom struct in their uAPI and are relying on struct 
> v4l2_params_buffer we can't just do sizeof(), so the idea was for this to provide a canonical way 
> for the size calculation to be done across both the kernel and userspace.
> 
> If we decide that it's worth keeping but want a user in this series to justify its inclusion, it 
> could be used in patches 2 and 3 - I'll reply to patch 2 in a second to indicate where.

Will it be used by userspace too for the Mali C55, or only by the kernel
driver ?

> [1] https://elixir.bootlin.com/linux/v6.17/source/include/uapi/linux/rkisp1-config.h#L1675
> [2] https://elixir.bootlin.com/linux/v6.17/source/include/uapi/linux/media/amlogic/c3-isp-config.h#L558>
>
> >> +
> >> +/**
> >> + * struct v4l2_params_buffer - V4L2 extensible parameters configuration
> >> + *
> >> + * This struct contains the configuration parameters of the ISP algorithms,
> > 
> > s/struct/structure/
> > 
> >> + * 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
> > 
> > I think you can drop "nor overlaps", nobody in their right mind should
> > think the blocks could be overlayed :-)
> > 
> >> + * the effective size, in bytes, of the @data buffer.
> >> + *
> >> + * @version: The parameters buffer version (driver-specific)
> >> + * @data_size: The configuration data effective size, excluding this header
> >> + * @data: The configuration data
> > 
> > Move the fields up just after the structure name.
> > 
> > Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> > 
> >> + */
> >> +struct v4l2_params_buffer {
> >> +	__u32 version;
> >> +	__u32 data_size;
> >> +	__u8 data[] __counted_by(data_size);
> >> +};
> >> +
> >> +#endif /* _UAPI_V4L2_ISP_H_ */

-- 
Regards,

Laurent Pinchart