linux-kernel - Re: [PATCH v5 8/8] media: Documentation: kapi: Add v4l2 generic ISP support

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Message-ID: <20251006011829.GC29231@pendragon.ideasonboard.com>
Date: Mon, 6 Oct 2025 04:18:29 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Jacopo Mondi <jacopo.mondi@...asonboard.com>
Cc: Dafna Hirschfeld <dafna@...tmail.com>, Keke Li <keke.li@...ogic.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Dan Scally <dan.scally@...asonboard.com>,
	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 8/8] media: Documentation: kapi: Add v4l2 generic ISP
 support

Hi Jacopo,

Thank you for the patch.

On Mon, Sep 15, 2025 at 07:18:17PM +0200, Jacopo Mondi wrote:
> Add to the driver-api documentation the v4l2-isp.h types and
> helpers documentation.
> 
> Reviewed-by: Daniel Scally <dan.scally@...asonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo.mondi@...asonboard.com>
> ---
>  Documentation/driver-api/media/v4l2-core.rst |  1 +
>  Documentation/driver-api/media/v4l2-isp.rst  | 37 ++++++++++++++++++++++++++++
>  MAINTAINERS                                  |  1 +
>  3 files changed, 39 insertions(+)
> 
> diff --git a/Documentation/driver-api/media/v4l2-core.rst b/Documentation/driver-api/media/v4l2-core.rst
> index ad987c34ad2a8460bb95e97adc4d850d624e0b81..a5f5102c64cca57b57b54ab95882b26286fb27de 100644
> --- a/Documentation/driver-api/media/v4l2-core.rst
> +++ b/Documentation/driver-api/media/v4l2-core.rst
> @@ -27,3 +27,4 @@ Video4Linux devices
>      v4l2-common
>      v4l2-tveeprom
>      v4l2-jpeg
> +    v4l2-isp

At what point we should structure the documentation. At one point :-)

> diff --git a/Documentation/driver-api/media/v4l2-isp.rst b/Documentation/driver-api/media/v4l2-isp.rst
> new file mode 100644
> index 0000000000000000000000000000000000000000..d778aa799347bfd0a95bd6887dd944ddad0fe4d1
> --- /dev/null
> +++ b/Documentation/driver-api/media/v4l2-isp.rst
> @@ -0,0 +1,37 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +V4L2 generic ISP parameters and statistics support
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +ISP configuration parameters and statistics are processed and collected by
> +drivers and exchanged with userspace through data types that usually
> +reflect the ISP peripheral registers layout.
> +
> +Each ISP driver defines its own metadata format for parameters and statistics,
> +and exposing the registers layout in the format definition, part of the Linux
> +kernel uAPI/uABI interface, makes it really hard, if not impossible, to extend
> +the format in a backward compatible way to support new hardware blocks or
> +different revisions of the same peripheral IP.
> +
> +For these reasons Video4Linux2 defines generic types for ISP configuration
> +parameters and statistics with a set of associated helpers to support drivers
> +and users using generic types.
> +
> +Generic ISP configuration parameters
> +====================================
> +
> +Drivers can use the generic and extensible configuration parameters format by
> +re-using the types defined in the include/uapi/linux/media/v4l2-isp.h uAPI
> +header file.
> +
> +The uAPI header defines generic types which the driver is expected to re-use and
> +provide definitions for the types of supported ISP blocks, their control
> +flags and the expected maximum size of a buffer of parameters.
> +
> +When a driver receives a buffer of parameters from userspace it shall validate
> +it by using the helper functions and types available in include/media/v4l2-isp.h
> +before accessing the buffer to apply the parameters to the hardware registers.
> +

Same comments are for the UAPI, I think this will need a full rewrite later.

> +Generic ISP support driver documentation
> +========================================
> +.. kernel-doc:: include/media/v4l2-isp.h
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 5e0e4208ebe6c58a9ea0834e1ebb36abd2de06e1..b0c5e6c2b21a5d5ebc63d2ae8b5c1b68fa912b33 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -26414,6 +26414,7 @@ V4L2 GENERIC ISP PARAMETERS AND STATISTIC FORMATS
>  M:	Jacopo Mondi <jacopo.mondi@...asonboard.com>
>  L:	linux-media@...r.kernel.org
>  S:	Maintained
> +F:	Documentation/driver-api/media/v4l2-isp.rst
>  F:	Documentation/userspace-api/media/v4l/extensible-parameters.rst
>  F:	drivers/media/v4l2-core/v4l2-isp.c
>  F:	include/media/v4l2-isp.h

-- 
Regards,

Laurent Pinchart