Re: [PATCH v8 23/38] media: uapi: ccs: Add media bus code for MIPI CCS embedded data

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: linux-media@vger.kernel.org, tomi.valkeinen@ideasonboard.com,
	bingbu.cao@intel.com, hongju.wang@intel.com, hverkuil@xs4all.nl,
	Andrey Konovalov <andrey.konovalov@linaro.org>,
	Jacopo Mondi <jacopo.mondi@ideasonboard.com>,
	Dmitry Perchanov <dmitry.perchanov@intel.com>,
	"Ng, Khai Wen" <khai.wen.ng@intel.com>,
	Alain Volmat <alain.volmat@foss.st.com>
Subject: Re: [PATCH v8 23/38] media: uapi: ccs: Add media bus code for MIPI CCS embedded data
Date: Thu, 21 Mar 2024 18:49:14 +0200	[thread overview]
Message-ID: <20240321164914.GD9582@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20240313072516.241106-24-sakari.ailus@linux.intel.com>

Hi Sakari,

Thank you for the patch.

On Wed, Mar 13, 2024 at 09:25:01AM +0200, Sakari Ailus wrote:
> Add new MIPI CCS embedded data media bus code
> (MEDIA_BUS_FMT_CCS_EMBEDDED).
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  .../media/v4l/subdev-formats.rst              | 28 +++++++++++++++++++
>  include/uapi/linux/media-bus-format.h         |  3 ++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/subdev-formats.rst b/Documentation/userspace-api/media/v4l/subdev-formats.rst
> index cbd475f7cae9..c8f982411e70 100644
> --- a/Documentation/userspace-api/media/v4l/subdev-formats.rst
> +++ b/Documentation/userspace-api/media/v4l/subdev-formats.rst
> @@ -8564,3 +8564,31 @@ and finally the bit number in subscript. "X" indicates a padding bit.
>        - X
>        - X
>        - X
> +
> +.. _MEDIA-BUS-FMT-CCS-EMBEDDED:
> +
> +MIPI CCS Embedded Data Formats
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +`MIPI CCS <https://www.mipi.org/specifications/camera-command-set>`_ defines a
> +metadata format for sensor embedded data, which is used to store the register
> +configuration used for capturing a given frame. The format is defined in the CCS
> +specification. The media bus code for this format is
> +``MEDIA_BUS_FMT_CCS_EMBEDDED``.
> +
> +The CCS embedded data format definition includes three levels:
> +
> +1. Padding within CSI-2 bus :ref:`Data unit <media-glossary-data-unit>` as

s/Data unit/Data Unit/

> +   documented in the MIPI CCS specification.
> +
> +2. The tagged data format as documented in the MIPI CCS specification.
> +
> +3. Register addresses and register documentation as documented in the MIPI CCS
> +   specification.
> +
> +The format definition shall be used only by devices that fulfill all three
> +levels above.

Hmmmm... Do we need to mandate level 3 ? There are lots of sensors that
comply with the first two levels but have their own register set. Would
you like a sensor-specific embedded data format for each of them ? If
so, how would we document it without essentially copying the datasheet ?

> +
> +This mbus code are only used for "2-byte simplified tagged data format" (code
> +0xa) but their use may be extended further in the future, to cover other CCS
> +embedded data format codes.
> diff --git a/include/uapi/linux/media-bus-format.h b/include/uapi/linux/media-bus-format.h
> index d4c1d991014b..03f7e9ab517b 100644
> --- a/include/uapi/linux/media-bus-format.h
> +++ b/include/uapi/linux/media-bus-format.h
> @@ -183,4 +183,7 @@
>  #define MEDIA_BUS_FMT_META_20			0x8006
>  #define MEDIA_BUS_FMT_META_24			0x8007
>  
> +/* Specific metadata formats. Next is 0x9002. */
> +#define MEDIA_BUS_FMT_CCS_EMBEDDED		0x9001
> +
>  #endif /* __LINUX_MEDIA_BUS_FORMAT_H */

-- 
Regards,

Laurent Pinchart