linux-kernel - Re: [PATCH v3 1/5] docs: uapi: media: Document Raspberry Pi NV12 column format

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Message-ID: <b1d8b6407bcaea4e12ff1c6c206c8d3b591ac2a9.camel@ndufresne.ca>
Date: Fri, 23 May 2025 20:30:17 -0400
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Dave Stevenson <dave.stevenson@...pberrypi.com>, Sakari Ailus	
 <sakari.ailus@...ux.intel.com>, Laurent Pinchart	
 <laurent.pinchart@...asonboard.com>, Mauro Carvalho Chehab
 <mchehab@...nel.org>,  Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,  Florian Fainelli
 <florian.fainelli@...adcom.com>, Broadcom internal kernel review list	
 <bcm-kernel-feedback-list@...adcom.com>, John Cox
 <john.cox@...pberrypi.com>,  Dom Cobley <dom@...pberrypi.com>, review list
 <kernel-list@...pberrypi.com>, Ezequiel Garcia	
 <ezequiel@...guardiasur.com.ar>
Cc: John Cox <jc@...esim.co.uk>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-rpi-kernel@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/5] docs: uapi: media: Document Raspberry Pi NV12
 column format

Le mercredi 23 avril 2025 à 18:20 +0100, Dave Stevenson a écrit :
> The Raspberry Pi HEVC decoder uses a tiled format based on
> columns for 8 and 10 bit YUV images, so document them as
> NV12MT_COL128 and NV12MT_10_COL128.
> 
> Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> ---
>  .../userspace-api/media/v4l/pixfmt-yuv-planar.rst  | 42 ++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst b/Documentation/userspace-
> api/media/v4l/pixfmt-yuv-planar.rst
> index b788f6933855..b5b590f234b0 100644
> --- a/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> +++ b/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> @@ -827,6 +827,48 @@ Data in the 12 high bits, zeros in the 4 low bits, arranged in little endian ord
>        - Cb\ :sub:`11`
>        - Cr\ :sub:`11`
>  
> +V4L2_PIX_FMT_NV12MT_COL128 and V4L2_PIX_FMT_NV12MT_10_COL128
> +------------------------------------------------------------
> +
> +``V4L2_PIX_FMT_NV12MT_COL128`` is a tiled version of
> +``V4L2_PIX_FMT_NV12M`` where the two planes are split into 128 byte wide columns
> +of Y or interleaved CbCr.
> +
> +V4L2_PIX_FMT_NV12MT_10_COL128 expands that as a 10 bit format where 3 10 bit
> +values are packed into a 32bit word. A 128 byte wide column therefore holds 96
> +samples (either Y or interleaved CrCb). That effectively makes it 6 values in a
> +64 bit word for the CbCr plane, as the values always go in pairs.

Could be nice to mention that this has a verticalement alignment of 8, allowing
to represent it as a 128x8 tiled format with a column layout. This was handy for
the GStreamer integration your showed me.

Nicolas

> +
> +Bit-packed representation.
> +
> +.. tabularcolumns:: |p{1.2cm}||p{1.2cm}||p{1.2cm}||p{1.2cm}|p{3.2cm}|p{3.2cm}|
> +
> +.. flat-table::
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths: 8 8 8 8
> +
> +    * - Y'\ :sub:`00[7:0]`
> +      - Y'\ :sub:`01[5:0] (bits 7--2)` Y'\ :sub:`00[9:8]`\ (bits 1--0)
> +      - Y'\ :sub:`02[3:0] (bits 7--4)` Y'\ :sub:`01[9:6]`\ (bits 3--0)
> +      - unused (bits 7--6)` Y'\ :sub:`02[9:4]`\ (bits 5--0)
> +
> +.. tabularcolumns:: |p{1.2cm}||p{1.2cm}||p{1.2cm}||p{1.2cm}|p{3.2cm}|p{3.2cm}|
> +
> +.. flat-table::
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths: 12 12 12 12 12 12 12 12
> +
> +    * - Cb\ :sub:`00[7:0]`
> +      - Cr\ :sub:`00[5:0]`\ (bits 7--2) Cb\ :sub:`00[9:8]`\ (bits 1--0)
> +      - Cb\ :sub:`01[3:0]`\ (bits 7--4) Cr\ :sub:`00[9:6]`\ (bits 3--0)
> +      - unused (bits 7--6) Cb\ :sub:`02[9:4]`\ (bits 5--0)
> +      - Cr\ :sub:`01[7:0]`
> +      - Cb\ :sub:`02[5:0]`\ (bits 7--2) Cr\ :sub:`01[9:8]`\ (bits 1--0)
> +      - Cr\ :sub:`02[3:0]`\ (bits 7--4) Cb\ :sub:`02[9:6]`\ (bits 3--0)
> +      - unused (bits 7--6) Cr\ :sub:`02[9:4]`\ (bits 5--0)
> +
>  
>  Fully Planar YUV Formats
>  ========================