linux-kernel - Re: [PATCH 3/5] docs: uapi: media: Add common documentation of tiled NV15

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Date:   Mon, 7 Aug 2023 13:37:23 +0200
From:   Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To:     Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     kernel@...labora.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] docs: uapi: media: Add common documentation of tiled
 NV15

Hi Nicolas,

W dniu 4.08.2023 o 21:27, Nicolas Dufresne pisze:
> This way we don't have to repeat over and over how the pixels are
> packed in NV15.
> 
> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>
> ---
>   .../media/v4l/pixfmt-yuv-planar.rst           | 79 ++++++++++++++++---
>   1 file changed, 68 insertions(+), 11 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst b/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> index 1d43532095c0..052927bd9396 100644
> --- a/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> +++ b/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> @@ -373,10 +373,74 @@ two non-contiguous planes.
>   Tiled NV15
>   ----------
>   
> -``V4L2_PIX_FMT_NV15_4L4`` Semi-planar 10-bit YUV 4:2:0 formats, using 4x4 tiling.
> -All components are packed without any padding between each other.
> -As a side-effect, each group of 4 components are stored over 5 bytes
> -(YYYY or UVUV = 4 * 10 bits = 40 bits = 5 bytes).
> +Semi-planar 10-bit YUV 4:2:0 formats. All components are packed
> +without any padding between each other. Each pixels occupy 15 bits

Maybe "Each pixel group"?



> +and are usually stored in group of 4 components stored over 5 bytes
> +(YYYY or UVUV = 4 * 10 bits = 40 bits = 5 bytes) or partitioned into
> +upper 8 bit and lower 2 bits.
> +
> +.. flat-table:: Sample of 4 NV15 luma pixels
> +    :header-rows:  2
> +    :stub-columns: 0
> +
> +    * -
> +      - 8
> +      - 7
> +      - 6
> +      - 5
> +      - 4
> +      - 3
> +      - 2
> +      - 1
> +      - 0
> +    * - byte 0
> +      - Y'\ :sub:`0:0`
> +      - Y'\ :sub:`0:1`
> +      - Y'\ :sub:`0:2`
> +      - Y'\ :sub:`0:3`
> +      - Y'\ :sub:`0:4`
> +      - Y'\ :sub:`0:5`
> +      - Y'\ :sub:`0:6`
> +      - Y'\ :sub:`0:7`

So byte 0 contains Y0, bits 0..7 but then...

> +    * - byte 1
> +      - Y'\ :sub:`0:8`
> +      - Y'\ :sub:`0:9`
> +      - Y'\ :sub:`1:0`
> +      - Y'\ :sub:`1:1`
> +      - Y'\ :sub:`1:2`
> +      - Y'\ :sub:`1:3`
> +      - Y'\ :sub:`1:4`
> +      - Y'\ :sub:`1:5`
> +    * - byte 2
> +      - Y'\ :sub:`1:6`
> +      - Y'\ :sub:`1:7`
> +      - Y'\ :sub:`1:8`
> +      - Y'\ :sub:`1:9`
> +      - Y'\ :sub:`2:0`
> +      - Y'\ :sub:`2:1`
> +      - Y'\ :sub:`2:2`
> +      - Y'\ :sub:`2:3`
> +    * - byte 3
> +      - Y'\ :sub:`2:4`
> +      - Y'\ :sub:`2:5`
> +      - Y'\ :sub:`2:6`
> +      - Y'\ :sub:`2:7`
> +      - Y'\ :sub:`2:8`
> +      - Y'\ :sub:`2:9`
> +      - Y'\ :sub:`3:0`
> +      - Y'\ :sub:`3:1`
> +    * - byte 4
> +      - Y'\ :sub:`3:2`
> +      - Y'\ :sub:`3:3`
> +      - Y'\ :sub:`3:4`
> +      - Y'\ :sub:`3:5`
> +      - Y'\ :sub:`3:6`
> +      - Y'\ :sub:`3:7`
> +      - Y'\ :sub:`3:8`
> +      - Y'\ :sub:`3:9`
> +
> +``V4L2_PIX_FMT_NV15_4L4`` stores pixels in 4x4 tiles, and stores tiles linearly
> +in memory.
>   
>   ``V4L2_PIX_FMT_NV12M_10BE_8L128`` is similar to ``V4L2_PIX_FMT_NV12M`` but stores
>   10 bits pixels in 2D 8x128 tiles, and stores tiles linearly in memory.
> @@ -385,13 +449,6 @@ The image height must be aligned to a multiple of 128.
>   The layouts of the luma and chroma planes are identical.
>   Note the tile size is 8bytes multiplied by 128 bytes,
>   it means that the low bits and high bits of one pixel may be in different tiles.
> -The 10 bit pixels are packed, so 5 bytes contain 4 10-bit pixels layout like
> -this (for luma):
> -byte 0: Y0(bits 9-2)

...here it says byts 9-2? Is it a mistake or are you cleaning up the doc
and the table above is the correct version?

Regards,

Andrzej

> -byte 1: Y0(bits 1-0) Y1(bits 9-4)
> -byte 2: Y1(bits 3-0) Y2(bits 9-6)
> -byte 3: Y2(bits 5-0) Y3(bits 9-8)
> -byte 4: Y3(bits 7-0)
>   
>   ``V4L2_PIX_FMT_NV12_10BE_8L128`` is similar to ``V4L2_PIX_FMT_NV12M_10BE_8L128`` but stores
>   two planes in one memory.