Message-ID: <20251006095850.GC5944@pendragon.ideasonboard.com>
Date: Mon, 6 Oct 2025 12:58:50 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Dan Scally <dan.scally@...asonboard.com>
Cc: Jacopo Mondi <jacopo.mondi@...asonboard.com>,
	Dafna Hirschfeld <dafna@...tmail.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>,
	Antoine Bouyer <antoine.bouyer@....com>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 1/8] media: uapi: Introduce V4L2 generic ISP types

On Mon, Oct 06, 2025 at 10:51:33AM +0100, Daniel Scally wrote:
> On 06/10/2025 10:06, Laurent Pinchart wrote:
> > On Mon, Oct 06, 2025 at 09:46:26AM +0100, Daniel Scally wrote:
> >> On 06/10/2025 09:27, Laurent Pinchart wrote:
> >>> 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@...asonboard.com>
> >>>>>> Reviewed-by: Daniel Scally <dan.scally@...asonboard.com>
> >>>>>> Signed-off-by: Jacopo Mondi <jacopo.mondi@...asonboard.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@...asonboard.com>
> >>>>>> +L:	linux-media@...r.kernel.org
> >>>>>> +S:	Maintained
> >>>>>> +F:	include/uapi/linux/media/v4l2-isp.h
> >>>>>> +
> >>>>>>     VF610 NAND DRIVER
> >>>>>>     M:	Stefan Agner <stefan@...er.ch>
> >>>>>>     L:	linux-mtd@...ts.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@...asonboard.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
> >>
> >> I have used it in userspace too.
> > 
> > Any pointer to the code ?
> 
> I didn't post my commits to adapt the mali-c55 IPA to the extensible parameters, but it's basically 
> the same as Jacopo's patch here: 
> https://lists.libcamera.org/pipermail/libcamera-devel/2025-October/053567.html
> 
> And the change I made using the macro was in IPAMaliC55::fillParams():
> 
> -       memset(params, 0, sizeof(mali_c55_params_buffer));
> +       memset(params, 0, v4l2_params_buffer_size(MALI_C55_PARAMS_MAX_SIZE));

Given that the buffer should be sized for the worst case, wouldn't it be
better to memset .planes()[0].data().size() ?

> >>> 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@...asonboard.com>
> >>>>>
> >>>>>> + */
> >>>>>> +struct v4l2_params_buffer {
> >>>>>> +	__u32 version;
> >>>>>> +	__u32 data_size;
> >>>>>> +	__u8 data[] __counted_by(data_size);
> >>>>>> +};
> >>>>>> +
> >>>>>> +#endif /* _UAPI_V4L2_ISP_H_ */

-- 
Regards,

Laurent Pinchart

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