Message-ID: <71d2f967-7e7f-43d6-9f7e-28c7f438d03c@ideasonboard.com>
Date: Mon, 6 Oct 2025 11:26:22 +0100
From: Dan Scally <dan.scally@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...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

Hi Laurent

On 06/10/2025 10:58, Laurent Pinchart wrote:
> 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():

Just for context, that function currently is:

void IPAMaliC55::fillParams(unsigned int request,
			    [[maybe_unused]] uint32_t bufferId)
{
	struct mali_c55_params_buffer *params;
	IPAFrameContext &frameContext = context_.frameContexts.get(request);

	params = reinterpret_cast<mali_c55_params_buffer *>(
		buffers_.at(bufferId).planes()[0].data());
	memset(params, 0, sizeof(mali_c55_params_buffer));

	params->version = MALI_C55_PARAM_BUFFER_V1;

	for (auto const &algo : algorithms()) {
		algo->prepare(context_, request, frameContext, params);

		ASSERT(params->total_size <= MALI_C55_PARAMS_MAX_SIZE);
	}

	size_t bytesused = offsetof(struct mali_c55_params_buffer, data) + params->total_size;
	paramsComputed.emit(request, bytesused);
}

>>
>> -       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() ?

Won't buffers_.at(bufferId).planes()[0].size() be the same as 
v4l2_params_buffer_size(MALI_C55_PARAMS_MAX_SIZE)? I am under the impression that that size will 
come ultimately from .queue_setup() which will be setting the sizes with:

sizes[0] = v4l2_params_buffer_size(MALI_C55_PARAMS_MAX_SIZE);

In that sense I suppose that that would remove the need for v4l2_params_buffer_size() to be used in 
userspace and we could just fallback to struct_size_t() within the kernel though.

> 
>>>>> 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_ */
> 

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