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

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

On Sun, Oct 05, 2025 at 03:06:04AM +0300, Laurent Pinchart wrote:
> Hi Jacopo,
> 
> Thank you for the patch.
> 
> 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)

It occurred to me that, now that this is part of v4l2-isp.h, we should
probably prefer everything with v4l2_isp_. This would become
V4L2_ISP_PARAMS_FL_BLOCK_DISABLE, and same for the structures below.
Sorry for not noticing earlier.

> > +
> > +/*
> > + * 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).
> 
> > +
> > +/**
> > + * 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