linux-kernel - [PATCH 1/4] media: uapi: Clarify MBUS color component order for serial buses

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Message-Id: <20250612-csi-bgr-rgb-v1-1-dc8a309118f8@kernel.org>
Date: Thu, 12 Jun 2025 14:53:39 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Hans Verkuil <hverkuil@...all.nl>, Mats Randgaard <matrandg@...co.com>, 
 Alain Volmat <alain.volmat@...s.st.com>, 
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Hans Verkuil <hans.verkuil@...co.com>, 
 Dave Stevenson <dave.stevenson@...pberrypi.com>, 
 Maxime Ripard <mripard@...nel.org>
Subject: [PATCH 1/4] media: uapi: Clarify MBUS color component order for
 serial buses

The subdev format documentation has a subsection describing how to use
the media bus pixel codes for serial buses. While it describes the
sampling part well, it doesn't really describe the current convention
used for the components order.

Let's improve that.

Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 Documentation/userspace-api/media/v4l/subdev-formats.rst | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/subdev-formats.rst b/Documentation/userspace-api/media/v4l/subdev-formats.rst
index 2a94371448dc07e5c7097421bd82f42dcd7e21aa..8e92f784abd8123f9ea950f954a60af56ee76dbe 100644
--- a/Documentation/userspace-api/media/v4l/subdev-formats.rst
+++ b/Documentation/userspace-api/media/v4l/subdev-formats.rst
@@ -158,16 +158,18 @@ 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. For
-instance, both MEDIA_BUS_FMT_BGR888_1X24 and MEDIA_BUS_FMT_BGR888_3X8 are used
-on parallel busses for transferring an 8 bits per sample BGR data, whereas on
-serial busses the data in this format is only referred to using
-MEDIA_BUS_FMT_BGR888_1X24. This is because there is effectively only a single
-way to transport that format on the serial busses.
+parallel format that transfers a sample on a single clock cycle is used. The
+color component order used is the same used on the serial bus. For instance,
+both MEDIA_BUS_FMT_BGR888_1X24 and MEDIA_BUS_FMT_BGR888_3X8 are used on parallel
+busses for transferring an 8 bits per sample BGR data, whereas on serial busses
+the data in this format is only referred to using MEDIA_BUS_FMT_BGR888_1X24,
+with BGR meaning that the blue component is transmitted first, then green, then
+red. This is because there is effectively only a single way to transport that
+format on the serial busses.
 
 Packed RGB Formats
 ^^^^^^^^^^^^^^^^^^
 
 Those formats transfer pixel data as red, green and blue components. The

-- 
2.49.0