linux-kernel - Re: [PATCH v4 02/10] media: Add Y012 video format

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Message-ID: <fbb6cbfd-9c40-7cf1-5790-eb3a14e12296@xs4all.nl>
Date:   Tue, 21 Mar 2023 11:39:02 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Ming Qian <ming.qian@....com>, mchehab@...nel.org,
        mirela.rabulea@....nxp.com
Cc:     shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, xiahong.bao@....com, linux-imx@....com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 02/10] media: Add Y012 video format

On 14/03/2023 11:08, Ming Qian wrote:
> Y012 is a luma-only formats with 12-bits per pixel,
> expanded to 16bits.
> Data in the 12 high bits, zeros in the 4 low bits,
> arranged in little endian order.
> 
> Signed-off-by: Ming Qian <ming.qian@....com>
> ---
>  .../userspace-api/media/v4l/pixfmt-yuv-luma.rst   | 15 +++++++++++++++
>  drivers/media/v4l2-core/v4l2-ioctl.c              |  1 +
>  include/uapi/linux/videodev2.h                    |  1 +
>  3 files changed, 17 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst b/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> index 62078a01de76..7888151f2cd4 100644
> --- a/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> +++ b/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> @@ -103,6 +103,17 @@ are often referred to as greyscale formats.
>        - ...
>        - ...
>  
> +    * .. _V4L2-PIX-FMT-Y012:
> +
> +      - ``V4L2_PIX_FMT_Y012``
> +      - 'Y012'
> +
> +      - Y'\ :sub:`0`\ [3:0] `0000`
> +      - Y'\ :sub:`0`\ [11:4]
> +      - ...
> +      - ...
> +      - ...
> +
>      * .. _V4L2-PIX-FMT-Y14:
>  
>        - ``V4L2_PIX_FMT_Y14``
> @@ -146,3 +157,7 @@ are often referred to as greyscale formats.
>      than 16 bits. For example, 10 bits per pixel uses values in the range 0 to
>      1023. For the IPU3_Y10 format 25 pixels are packed into 32 bytes, which
>      leaves the 6 most significant bits of the last byte padded with 0.
> +
> +    For Y012 and Y12 formats, Y012 place its data in the 12 high bits, with

place -> places

> +    padding zeros in the 4 low bits, in contrast to Y12 format, which have

to Y12 -> to the Y12
have -> has

> +    its padding located in the most significant bits of the 16 bit word.
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 6489b67babfa..2cb485643562 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1307,6 +1307,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>  	case V4L2_PIX_FMT_Y6:		descr = "6-bit Greyscale"; break;
>  	case V4L2_PIX_FMT_Y10:		descr = "10-bit Greyscale"; break;
>  	case V4L2_PIX_FMT_Y12:		descr = "12-bit Greyscale"; break;
> +	case V4L2_PIX_FMT_Y012:		descr = "12-bit Greyscale"; break;

I don't really like having two identical pixelformat names, but I can't
think of a good way to describe the difference.

Perhaps "12-bit Greyscale (bits 15-4)"?

Regards,

	Hans

>  	case V4L2_PIX_FMT_Y14:		descr = "14-bit Greyscale"; break;
>  	case V4L2_PIX_FMT_Y16:		descr = "16-bit Greyscale"; break;
>  	case V4L2_PIX_FMT_Y16_BE:	descr = "16-bit Greyscale BE"; break;
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index f83a9d1210fb..db06d4c4f008 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -586,6 +586,7 @@ struct v4l2_pix_format {
>  #define V4L2_PIX_FMT_Y6      v4l2_fourcc('Y', '0', '6', ' ') /*  6  Greyscale     */
>  #define V4L2_PIX_FMT_Y10     v4l2_fourcc('Y', '1', '0', ' ') /* 10  Greyscale     */
>  #define V4L2_PIX_FMT_Y12     v4l2_fourcc('Y', '1', '2', ' ') /* 12  Greyscale     */
> +#define V4L2_PIX_FMT_Y012    v4l2_fourcc('Y', '0', '1', '2') /* 12  Greyscale     */
>  #define V4L2_PIX_FMT_Y14     v4l2_fourcc('Y', '1', '4', ' ') /* 14  Greyscale     */
>  #define V4L2_PIX_FMT_Y16     v4l2_fourcc('Y', '1', '6', ' ') /* 16  Greyscale     */
>  #define V4L2_PIX_FMT_Y16_BE  v4l2_fourcc_be('Y', '1', '6', ' ') /* 16  Greyscale BE  */