Re: [PATCH 1/1] v4l: Documentation: Serial busses use parallel mbus codes

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On 8/13/19 1:30 PM, Sakari Ailus wrote:
> When the support for serial busses was introduced in V4L2, it was decided
> to use the existing parallel bus media bus pixel codes to describe them.
> While this was a practical choice at the time, it necessitates choosing
> which one of the many parallel mbus pixel codes to use, for on the serial
> busses these formats are effectively all equivalent.
> 
> The practice has always been to use the pixel code that describes a bus
> that transfers a single sample per clock. Document this.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> ---
>  Documentation/media/kapi/csi2.rst               | 7 +++++++
>  Documentation/media/uapi/v4l/subdev-formats.rst | 4 ++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/Documentation/media/kapi/csi2.rst b/Documentation/media/kapi/csi2.rst
> index a7e75e2eba85a..c67736a15c45b 100644
> --- a/Documentation/media/kapi/csi2.rst
> +++ b/Documentation/media/kapi/csi2.rst
> @@ -72,3 +72,10 @@ the transmitter up by using the
>  :c:type:`v4l2_subdev_core_ops`->s_power() callback. This may take
>  place either indirectly by using :c:func:`v4l2_pipeline_pm_use` or
>  directly.
> +
> +Formats
> +-------
> +
> +The media bus pixel codes document parallel formats. Should the pixel data be
> +transported over a serial bus, the media bus pixel code that describes a
> +parallel format that transfers a sample on a single clock cycle is used.
> diff --git a/Documentation/media/uapi/v4l/subdev-formats.rst b/Documentation/media/uapi/v4l/subdev-formats.rst
> index ab1a48a5ae80b..d6b8b86a6daad 100644
> --- a/Documentation/media/uapi/v4l/subdev-formats.rst
> +++ b/Documentation/media/uapi/v4l/subdev-formats.rst
> @@ -85,6 +85,10 @@ formats in memory (a raw Bayer image won't be magically converted to
>  JPEG just by storing it to memory), there is no one-to-one
>  correspondence between them.
>  
> +The media bus pixel codes document parallel formats. Should the pixel data be
> +transported over a serial bus, the media bus pixel code that describes a
> +parallel format that transfers a sample on a single clock cycle is used.

I would add an example here along the lines of using MEDIA_BUS_FMT_BGR888_1X24
instead of MEDIA_BUS_FMT_BGR888_3X8.

Possibly in csi2.rst as well.

Regards,

	Hans

> +
>  
>  Packed RGB Formats
>  ^^^^^^^^^^^^^^^^^^
> 




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