Message-ID: <ecda9183-bd84-48fd-a1e0-e37b6dbacec6@ideasonboard.com>
Date: Mon, 6 Oct 2025 10:51:33 +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 10:06, 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));

Dan

> 
>>> 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_ */
> 

Powered by blists - more mailing lists